ditch the repair kit. alot of crits have pit area, put it there. If you get a flat, you are s.o.l. personally i'd call it a day but if u can fix and pump a flat in under 2 minutes and still ahve the drive to get back on and race thats up to you, most crits give you a free lap to a certain point.
for 20 minutes, i would say you wouldn;t need a water bottle. that being said i personally would have one with me with, about 1/4 full. its nice to be able to have a few sips if you do get thirsty, and gatorade does give you some energy.....sort of. you could always toss the empty bottle, but it really isnt that much weight. also be carefull of overhydrating prior to the race, that won't help. (i tried that once and ended up puking up stuff in my mouth and having to spit it out mid race. i had no water, so i had to taste vomit for another 10 minutes before the end of the race)
good luck, and have fun.