[Mechanic] Fishing

In most RPGs, there comes a point where you are grinding for levels. The drill looks like

1. Go grind some monsters for gold/exp
2. Return to inn to heal
3. Repeat

People continue doing it because they see a tangible increase in their power (as they level up) and an increase in numbers as they watch gold/exp go up.

Instead of the inn, you could introduce a minigame or mechanic (depending on how much you want to flesh it out) for fishing. Require characters to have bought some fishing rod (which could increase in quality the more you spend on it, providing improvement there) as well as bait (which could have variations in effects, such as what you can catch with each bait, how strongly it attaches fish that bite onto it, how quickly it attracts fish, etc).

Instead of the inn, give the players a lake or somewhere to fish. Let them either buy berries while they are in town (stocking up), or find them while they are out (as drops from monsters, or in bushes, or in trees, etc). Those berries, or whatever other bait you use, can directly translate into fish (when you fish), and the player's skill in fishing determines whether they get a small fish (that heals a little), a big fish (that heals a lot), a blue fish (that heals mana), etc. Of course, you can also stumble across treasure chests underground you can hook with sturdy bait/rods, and monsters that you can hook as well.

On the story side, this mechanic could sustain a party if they are away from town for a long time, such as if they are on an adventure (passing lakes with different kinds of fish), or in an open world (trying to stay close to water so they can continuously fish food), or stranded on an island, etc. It also lets players stock up what equates to potions for use in battles, too. 

If you flesh out the skill a lot, you could gain experience as you catch fish, that enables you to use different bait, different rods, catch different things, avoid monsters, be more efficient in your fishing, etc.