I work retail, too (my condolences lol) and we are only allowed to keep water out "on the floor" which must be kept discretely from view. Being that we only get one 20 minute break if we work up to 6½ hours, I find I absolutely need some beverage while out walking around (I can't necessarily wait for breaktime to roll around before I am permitted to go into the breakroom and hydrate myself.)
I buy store brand water bottles and drink plain, room temp water, but for long shifts I do use a mix-in generic, individual portion "fitness" powder. I find if I use the entire individual pack it tastes uber sweet like a jolly rancher, ugh, so I use half of an individual pack per 17oz water bottle. One entire individual mix-in pack has only 5 calories, plus basically some b vitamins. Although it looks very slightly cloudy, it still pretty much looks like plain water in a bottle, which is great for camouflage and conforming to store policy. It gives it some taste which is helpful. I find it keeps me feeling energetic without the caffeine. You might like it!
What kind of snacks or food do you bring to work? My go-tos are protein bars, Greek yoghurt, and plain almonds. I'm too lazy to pack a real lunch, lol. Work has been a diet minefield this holiday season, what with the potlucks, chili-cookoffs, dessert days, etc. I walked into work last night and I kid you not, it was "bring your favorite side dish to work." I was all like really, are y'all serious.
Good luck in retail
Very soon all of the stuff that seems overwhelming and new will just be second nature because of the repetition. This is a tough time of year to start retail, the toughest! Another few weeks (after the onslaught of returns are done) and we will be home free