This is as spoiler-free as you can get!
A Xenoblade Chronicles 3 canteen is useful for multiple reasons. It serves as a rest stop, which you can use to do all sorts of rest-stoppy things like add bonus XP and talk things over with your party for a chance at extra XP and more questlines. But the real thing that sets canteens apart from camps is the ability to learn new recipes for party member Manana. So make sure you make a point to hit every canteen you can!
Here’s a very early game (like first-few-hours-early) example!
Canteens are typically found in colonies
Colonies are by and large the “cities/towns” of Xenoblade Chronicles 3. Here you’ll find opportunities to gather up new quests, as well as some hidden caches (barrels full of useful items and equipment), and…canteens.
One of the first things you’ll want to do every time you locate a new colony is go to the canteen. If you aren’t sure if something is a canteen or not (if you’re judging whether or not to waste precious fast travel load time), you can simply highlight it on the map and it’ll appear on the screen with the full rundown. These can share the same “handshake” icon as camps, but it’ll say “canteen” in the rest spot description.
Just order whatever food is available
Once you’re at a canteen, buy the food available for a nominal gold fee. It’s OK if you’re overwriting a current effect (like the one shown here), you’re going to be learning the recipe to use forevermore in any camp.
By ordering new food, Manana (the party cook) will be able to replicate it on their own. You’ll want to gather as many recipes as possible so that you can use the one that suits your needs (like if you need an XP boost, or a class point [CP] boost to reach a certain milestone to clear a boss/optional encounter).
If you just caught this tip and haven’t ordered anything at a Xenoblade Chronicles 3 canteen, don’t worry! Just open up the world map and go to every canteen you’ve located, and order the food. Even if you’ve ordered it before, it’s OK: the cost is generally minimal and you could end up acquiring a new recipe you missed.
