My son's experience with those little saddle-paks is that one tends to lose the contents on the trail... the younger one used to stop & pick up what the older one dropped during a race. They both pretty much use medium sized hydration packs - the pockets on it should be big enough for your spare tubes & tools.
You should drink during a race, but, more importantly, begin to hydrate the day beofre the race (and not with beer!). Don't eat within 2-3 hours of racing, but when you have your breakfast, it wouldn't hurt to focus on thinks like pancakes or waffles with some eggs, or some oatmeal. You will need the carbs and the protein! Munch down an energy-type bar during the pre-race meeting. If your race does not offer a post-race meal, pack some food for after the race, because you will be hungry. Also, a really cheap alternative to those energy-gel packets are circus peanuts - those orange things - they're basically the same stuff as Gu.