A highly intelligent man or woman with whatever modern or genre knowledge you like wakes up one day in an RPG world, and they are the protagonist. They possess mystical elemental powers that are strengthened by slaying monsters. They regularly have epic story hooks thrown at them. Most importantly, they find various points in the world that allow them to 'save' at a specific place, and then 'restore' to the point in time that they saved with specific memories of what took place.
The world itself is medieval, and has most of the conventions one might expect in an RPG - it's mostly made up of feudal city-states ruled over by corrupt-ish monarchies and occasionally conquered by vast empires. Most of the land is beset by wandering magical of all kinds, some of which appear to be sentient, and almost all of which are violent and dangerous. Quality of life is low for the average person, even without the presence of the ancient evil that is presumably approaching at some point.
The protagonist is benevolent and utilitarian. They set about attempting to improve the world's quality of life and reduce suffering as much as possible. They don't just want to stop the ancient evil (though that might be an instrumental goal.) They want to use their newfound power to do real and active good, and ensure that the citizens of the world live as well as they possibly can.
The protagonist can (and is encouraged to) 'munchkin' their powers as much as necessary in order to achieve this goal. They can use spells that are typically restricted to combat (such as cure spells) in any context. They can save and restore to solve arbitrarily to explore the possibility-space around any decision, up to a limit of their own patience - for example, they could use saving to solve arbitrarily difficult math problems in an instant, or to find the perfect time to sneak into the evil overlord's palace and place botulinum toxin in his tea. They can use genre knowledge to their advantage, though of course this may backfire once in a while. Save and restore seems like by far the most useful power, but there might be obscure uses for other RPG powers that often go unconsidered.
What techniques might the protagonist use to improve the state of their world? Would they try to take over the existing governments? Try to mass-produce CURE spells and EXP for the general public? Civilize the monster population that controls the vast majority of the arable land?
Bonus points: How might a similarly savvy evil overlord stop a character with powers like this, if they identified him or her early on? Assume for simplicity that the protagonist only has one save 'slot' at a time, so once they've saved at a point they cannot revert to before that point.