I think a lot depends on how much you sweat. If you sweat a lot you're going to need to replace those fluids. If I know I'm going to be going on a long ride I'll hydrate a lot before I go. I've found that carrying two bottles in cages will get me through a 40 mile ride without needing to stop. If I'm planning on riding more than 40 miles I'll use my camelback (3L). Get a seatbag for your tube and tools. Get a jersey or two. They're more comfortable and who cares what you look like. When I started riding a few years ago I weighed 280# at 5'10". I looked like a sausage but I didn't care. I felt good riding and I knew it would eventually payoff healthwise, and it did and continues to do so.