On our boat, we too have towels, sunscreen, bug spray(not often needed), diet caffeine free pop(wifey has heart issues) PBR beer and water.
Eating depends on who it is and what we're doing.
So cruising around with friends/family, maybe pulling the tube, if they have something in particular they drink that I don't have, they're welcome to bring it.
Fishing means you bring your own pole or two, your own tackle and/or bait as long as it doesn't take up half the boat. Fishing buddies that drink prodigious amounts of beer usually chip in and bring a supply of PBR to help augment the supply on the boat.
One "Velcroed Niece" often brings treats of some kind, and she's been on the boat often enough that she pretty much acts as a First Mate, bringing out stowed items, or helping stow them away properly along with tying up or helping cast off lines when leaving the slip.
One couple frequently brings their home made chicken salad sandwiches with them along with some chips and cookies. Not always, but just often enough to be gracious and not be mooches.
A while back, I took the neighborhood little old ladies, all but one of whom is a widow out for a cruise.
It was my treat, including Margarita's, Turkey Sandwiches, fresh from the garden cantaloupe and cucumbers.
One of them wanted to fish, so we hit up one of my favorite holes and after half a dozen nice catfish, which I later cleaned and bagged for her, putting them on ice in the cooler,) she suddenly got a shocked look on her face when the Lake Cops cruised up to do a License/Creel Check. She started stammering about not having a license

, and I simply commented "This is one of those times when being a Seasoned Citizen pays off, you're old enough you don't have to have one.
Basically, I'm laid back enough that anyone I've invited on my toon knows that it's my treat unless there's something they graciously offer to bring, or if they bring something they like that I don't keep on board.