what kind of water bottle you have makes the difference in how you cart it around. for a sigg or another with a loop top, it's easy to just buy a carabiner and hook it to your bag or belt loop. if you buy disposable bottles, you can buy a strap there that you hook around your neck [think a lanyard or purse strap] and adjust around the water bottle. they also have another variant that's a coozy that's attached to a strap that you can put around your neck or attach to your belt. if you're confused by that description, just start looking at cast members, particularly ones that are in sunny spots like the people who park you or the first agent p station on your way to the world showcase and most of those stationary castmembers will have one of the disposable water bottle holders.
the only thing you can't bring in is glass. i have seen people bringing a full rotisserie chicken into the food and wine festival. in the plastic container you buy it in at the grocery store. you can bring in full coolers, soft coolers, pretty much anything that isn't glass or a weapon.
at epcot in the basement of the land you'll find a ton of grab and go options. they have salads, fruit and cheese plates, hummus plates, salad wraps, salads, hard boiled eggs and so forth. you can go on the land ride to see where some of the veggies are grown while you are down there.
disney's website or allears.net
has the food and wine festival menu up, though all ears posts pics of the prices. you can also find regular menu items there as well. the food and wine portions are tiny and the regular stuff is more overpriced than overportioned [though the portions are larger than portions].
while at the food and wine fest, make it your goal to do at least two laps [if not more] around the lagoon. i've done well over 10,000 steps in just a few hours by making sure to make circles.
if you stick to table service, you'll have more options and a little lighter fare. the self serve places tend to be heavily fried and fries. the sit down places should be able to handle any accommodations provided it's on the menu [ie, if they have mushrooms, they'll happily add mushrooms to your dish for you]. and if you prefer quality stuff, the tutto gusto wine cellar in itlay has excellent anitpato stuff. it's not the lowest calorie food ever invented, but it's excellent quality and well balanced. plus, it's great to share with the table and the portions are fairly small.