A reasonably health guy/gal shouldn't have too much problem with doing 50 miles but it'd make things a lot easier if you get some rides within the 20 to 40 mile range before hand.
Would one ride a week be enough? Go out and do 40 miles this weekend and let us know how you do. If you do fine then the answer is yes... one ride per week will be fine, otherwise the answer is you'd probably be better off riding a few times a week. If you don't ride that much anyway, any time on the bike during the week will help even if it's only 30 minutes riding at a fairly brisk pace. Combine it with a longer ride on the weekend.
A couple of big 20 to 24oz water bottles should be fine and if you already have bottle cages on the bike then they'll fit. I'm always wary of using hydration packs like the Camelbak with anything other than water as they can be a pain to clean. "Sports drinks" tend to be great breading grounds for bacteria and the like - they like the stuff as much as we do on the bike 😉
Cereal bars are pretty good to snack on while out on the bike. Bananas and even jam sandwiches will do it if that's what you like. The local bike shop should have some good energy drinks too. Don't go overboard though. Take a look at the label on the stuff you eat and try not to consume more than 300Kcals per hour when riding. You don't need more than that and any more may increase the risk of gas and discomfort. That last thing you want is sharted shorts.
Whatever you decide to munch on, try it before the ride - preferably on a ride closer to the 40 to 50 mile mark. Sometimes what you eat after a couple of hours on the bike doesnt taste as good as it did when you stood in the kitchen before the ride.