(Assuming the shower is running. Any temperature.)
The best I could come up with was a hot soup, but eventually you'll get more water then broth. There has to be a better food out there for those hungry showers!
I enjoy eating peaches in the shower
Any messy fruit, really, but stone fruits in general.
You can just shamelessly get in there, get that nectar all over your face, and enjoy it.
Probably more enjoyable if you have a beard and need to eat carefully.
I no longer drink, so this is like my shower beer now.
I prefer to run a hot bath with a bunch of bouillon cubes. I bring salad and breadsticks in with me for the unlimited experience Olive Garden promises, but refuses to actually provide paying customers.
There's the classic shower beer, and that's actually really fun. Like others said, be careful & if you want to be extra cautious, aluminum cans only or poured into a stainless steel vessel.
When I was a fat little teen, I somehow heard the idea of eating potato chips in the shower. I tried it & it was oddly satisfying. They were Ruffles. I only did it once or twice total, it would be kind of weird to do all the time.
BBQ on the bone - I haaate messy meals, so let's set up a table with slaw, taters and a nice rack slathered in sauce, get naked, and turn on the water.
curry. It may not appear ideal at first glance: water sprays on that and your flavor goes down the drain, literally. HOWEVER, with careful placement of the food container, you could effectively minimize the amount of water getting into your curry, minimizing loss of flavor. If your curry is too hot and you start to sweat, you can simply turn the tap colder to cool yourself down while you eat. When you're done, you don't need a finger bowl to clean your hands either, just run them under the shower water. Best enjoyed with rice, as the roti will get too soggy.
Something dry that even in hot humid air won't spoil quickly.
Cheese seems like a good bet. Certain cooked and cured meats similarly; salami or beef jerky, cooked sausages etc.
But ultimately why would you eat in the shower? The real problem is either time management issue or eating too much of you really need to cram food in your gob while showering. Also would waste more water and time in the shower if you're both eating and cleaning yourself.
Its the sort of seemingly innocuous question that actually shows you maybe should be taking a long hard look at your life priorities. The shower is a good place to think about that, maybe while chewing on a block of cheddar cheese.