Imagine something like a 'Stargate scenario'. The modern military has a means to send small squads to other worlds populated by people. The majority of these people will be at medieval or lower technological level, though more advanced societies will be found. They want to arm these small squads to handle most situations when making first contact, including hostile ones.
These squads will have modern weaponry, which will obviously be a significant threat to any potential hostile medieval people; however, they don't want first contact to involve the military massacring a primitive people who showed potential hostility, so resorting to superior firepower is a means of last resort. Still a bow and arrow can be just as fatal to a modern man, and if the primitives don't know what an assault rifle can do, and thus are not afraid of it, there is little to discourage potentially hostile people from attacking a seemingly undefended and outnumbered squad.
Having recognized the potential threat our military is looking to better equip their squads to deal with potential hostile primitives without resorting to lethal force. I'm looking for how the military will best equip their squads for handling this situation.
Keep in mind that they are limited in how much they can send in one trip, both in size (has to fit through the portal) and total mass they can send at one time; so large armored convoys or large number of units are not really viable. They also may run into more advanced people who are considered the greater threat, and so they don't want to weigh down their squads with too much anti-arrow technology if it proves cumbersome to carry around when dealing with more advanced hostiles.
They don't have any kind of prime directive. Having said that they have an explicit policy against trying to play god, or otherwise using technology to convince the natives they have some sort of magical powers. They must attempt to explain any ability they have are simply advanced technology whenever possible, and generally try not to screw up the primitive's too much.
Communication/language issues may or may not be a problem, many of the primitives share one of a few common languages that they will have people trained to communicate in all of the standard languages in each reconnaissance group, but some of the people may have their own language that can not be translated.
There are two potential situations I'm looking at how they military would equip themselves.
1) how do they equip the original reconnaissance forces, the ones that know little about the location they are traveling to. This group won't know how advanced any natives may be, and need to stay flexible and not present an overly aggressive appearance. This group may also want to include equipment to allow for discouraging primitives from starting hostile encounters (short of shooting them), such as flash-bang grenades or other instruments to prove they are better equipped for a fight without having to kill anyone.
2) How would they equip a team when traveling to a land they know contains primitives, particularly potential hostile ones, when it would make sense to commit to fully armored anti-infantry setup. Can they be so well armored as to be nearly invincible to swords and arrows? Enough that they will feel comfortable using less-lethal weaponry to subdue instead of kill a hostile tribe if they need to?