In every system, there are rewards keyed by the system itself; experience or other character advancement points, mechanical bonuses built into the system as advancement, and special items that offer some defined mechanical bonus, like a +1 longsword in Pathfinder or a smartlink-modified plasma rifle in Eclipse Phase. Some offer more nebulous rewards, still tied to a mechanical effect – increases in a social score that give the character access to higher levels of society. In many popular games, these are the sum of the rewards available.
That doesn’t need to be the case; while premade campaigns tend to be reliant on those, and adventure modules certainly need to keep to familiar rewards to avoid injecting problematic things into home campaigns, but there’s nothing to restrict a GM from adding unusual rewards. This can, in games where the players rely on software to help track things, cause problems as the software isn’t designed to accept nonstandard modifications without a lot of effort (which has plagued my players since around level 4 or 5), but the thematic effects can be highly rewarding.
Consider a game where there’s no social mechanics, with a feudal kind of campaign setting. Giving your players an official title granted by the local lord or by the church of the land that has no mechanical effect but permits them to introduce them as a Lord or Lady or Holy Knight, garnering an appropriate degree of awe (or sneering) from NPCs can have a much more significant impact than being rewarded a generic magic item pulled from the sourcebook.
Similarly, giving the players an item but making it so that it has history, a story, and perhaps a name can give them something much more material than a generic item, however powerful. The Torch of Abeyance might end up meaning more to a character who gets it than a +2 flaming burst club, if presented with the mythos of a hero who fought to civilize the lands where the characters now dwell.
Mechanical bonuses that break the rules of the game can also be interesting; one character in my Pathfinder home game has a Swim speed thanks to asking for a boon from the god of the seas after rescuing him from captivity. Rather than it simply being a generic swim speed, she transforms, her lower legs transforming into an eel-like shape when immersed in the water. This has resulted in a few amusing RP moments, as the character doesn’t like to talk about her transformation, and doesn’t care to exhibit it.
Likewise, each of the characters has developed into something of a demigod, and in the process I’ve given each of them a supernatural ability completely removed from the usual benefits of gaining character levels and mythic powers in the system; the cavalier can use dimension door three times each day, moving himself, his mount, and anyone on the horse when he does so. He’s put this to use to blip around in battle, charging enemies from unexpected angles and bypassing obstacles in ways that make him larger than life without breaking the fun of the game itself.
The trick of it is to look for things where you might want to offer players a reward and to ask what you can offer them that might appeal to them without delaying their progression through the game or breaking the game’s appeal for the players. Something as simple as the character group developing a reputation that causes some enemies to surrender before combat even becomes a question, or drawing free drinks and cheering villagers when they ride into town can add a huge amount of satisfaction for players.
Give it some consideration for your next game!