There's a vast distance between the "common" monotheistic god, which usually is omniscient and omnipotent, and the old polytheistic gods, which were for sure far superior than human but they had a lot of limitations and only some specific powers.
With the current technology, one single person can't perform such a full scale "miracle" as the plagues of Egypt, therefore can't be perceived as an almighty god. On the other hand, one single person can for sure impersonate a polytheistic-level god and can definitely be seen as a demi-god without a lot of effort. I assume this person is (technically) a very skilled person, but alone he can't manage a nuclear power plant, use nuclear submarines, manage satellites, etc...
You stated that he can have any kind of material, weapon, etc... There are limitations in quantities?
You'll need without any doubt A LOT of energy but if you can carry whatever you want it's not a big deal: thousand tons of fuel, solar panels arrays, etc..
Granted that you have energy, you only have to decide how to astonish the other people. The possibilities are endless!
You can easily cure a lot of illness, or you can easily kill hundreds people with toxic gas (and you can wear a gas mask, then you'll survive when everyone else is painfully dying, therefore you are a god without any doubt).
You can charm or at least influence other people with drugs.
You can surprise people by setting "a bush on fire, without actually burn it up" using trivial led lights, this thing could be a total miracle for someone.
You can't walk on water but it will be easy to remain underwater for an unreasonable amount of time for a human being (small disposable oxygen tanks).
You can create fire "out of nowhere", also simulating psychic powers by using a small remote.
If you want to scare the people in a besieged castle you can just use a bunch of fireworks or, if you want to clarify your power once for all, you can use a couple of javelin missiles (actually i have to check if they need some kind of GPS assistance, in any case the old bazooka can also demolish a medieval castle).
Hercules god-like force? Military exoskeleton.
Lightning strike power like Zeus? Hidden weapon in your forearm, you point your hand, a thunder like sound and a small fire from your god powers occur, and the person you're facing is dead.
Do you want the power of curse someone? Infrared lased mounted on your crown, even a low power module: if someone dares to look at your face he will be blinded forever and no one will have a clue about the real cause (safety glasses for this wavelength are transparent in our visible spectrum, then they can be easily added to your helmet and no one will suspect that a transparent glass is actually helping you).
You want to create taboo zones in which no one should go? Claymore mines painted with your symbol? After some casualties everyone will learn that your symbol deserves respect.
Given that you are a trained pilot, which is not common but still reasonable, you can have your own dragon. I suggest the Kamov Ka-50, a single pilot attack helicopter, with a nice shape and an ejector seat (just in case.. I doubt that anything could harm this vehicle). With such a "beast" at your command you can rule every battlefield, and i really doubt that anyone else could have any chance to use this against you.
I stop here but the list could continue for days.
The main point is that EVERYTHING that's common for us will be astonishing for a medieval person, is not only a matter of "mechanical" power, even a stupid Polaroid can be seen as a miracle, especially for the person that will receive a portrait in almost not time.
With a gopro and a projector you can show to a crowd what happened to another army in a previous battle, and even if the enemy army has been obliterated in minutes, the most important concept is that you can evoke and show previous events. They will freak out only for this! Think about "L'Arrivée d'un train en gare de La Ciotat", which was the first projected film. In that occasion Der Spiegel wrote that the film "had a particularly lasting impact; yes, it caused fear, terror, even panic." I know that this description might be exaggerated, but remind that it was the state of the art of the current technology, not something that no one even theorized about.
You don't need the Death Star's death day to scare someone that never saw a firework.
A stupid hidden walkie talkie can let you hear secret meetings, therefore it seems that you can read minds, or you can spread your voice/orders in your temples or to your generals.
This reminds me of the army question.
It will be quite easy to build an army that can defeat every enemy and also that can't hurt you, the technology gap is so wide that they can have really unfair advantage against the enemy, but the "true" power is only on/in you.
- Even using the usual medieval items, your army can have better armors, better weapons, better siege tools, better tactics. You only have to share some knowledge with your blacksmiths and generals.
- Drugs and medicines: you will have an army of lucid berserkers, that can also be healed faster/better respect to the standard.
- If you don't want to risk your safety giving powerful poison to other people, you can still provide them "holy grenades" filled with tear gas. I doubt that a infantry charge could be properly finalized if your army has access to tear gas grenades, or at least the charge will be seriously crippled.
- With good radio equipment, in case of an exceptionally strong enemy, the god (you) can be prayed (called via radio) and with your flying beast (said helicopter) you can quickly reach the critical point, destroy the main enemy force, and then let your army to clean up the remaining forces.
With your god-like powers I presume you don't really need to build an army, everyone will try to be part of your army and I doubt that any opposing army can keep enough morale after a few tricks (if you are gracious) or after few missiles or gas bombs (if not).
Actually, I'll change my original statement: you definitely can be worshiped as an almighty god. You can win any war and kill every person. Basically no one can object your divine nature. They won't object because they truly think this, or you can simply remove any opponent and the history is as usual written by the winner.
To reply at L.Dutch:
IMHO you don't have to worry about that: good and bad, right or wrong are a moral concept. If you define the moral you can decide what's right and what's wrong.
Remember: you are the winner of every battlefield, then you can just "write the history" as you wish. Why not?
Moreover, some previously suggested actions could seem evil for us (us who?) and NOW but, for example, a thousand years ago actions like "torture already defeated enemies" or "burn people that use medical erbs" were ok, no big deal.
Actually, thinking about the catholic inquisition, precisely the god's emissaries performed some of the cruelest actions and no one bat an eye.
They had only money, army and propaganda and now look at the fortune they made along the centuries. You would have true god-like powers, you would be way more powerful than them.
even if we remove your possiblity to "redefine moral rules applying your power", the suggested actions aren't so strange for a god, so you don't actually have to redefine a lot.
The polytheistic-level gods usually behaves as an immature, selfish and cruel person with some superpowers.
The first examples that come to my mind:
- Prometheus, chained to a rock and doomed to be perennially devoured, because he wanted to help humans.
- Hercules, he massacred his family because his stepmother was pissed and drove him frenzy.
- The Gorgon Medusa, a former beautiful woman, mutated by Athena in a "monster with a horrifying visage that turned those who beheld her to stone". And why? Because she slept with (or has been raped by) Poseidon.
As you can see, at least in Greece, no one really cared about our current morality to worship some beings as gods. And even now, with our morality, if these people actually did exist, it wouldn't be so strange to worship them as the gods they are.
It's a non sense to discuss this in the case you are trying to be the monotheistic-level, almighty, omnipotent unic god.
I mean, here in Italy we are mostly Catholic and our god turned the water into blood, killed all the Egyptians first-borns, and once flooded the whole world, killing EVERYTHING except a bunch of people and few animals.
It's difficult for me to imagine something something more devastating and, since the flood didn't turn god into evil (which is, as previously said, only a relative concept), i don't know what action can do that.