i'm on my HS soccer team and this is what i do for abs:
50 regular crunches
50 right side-crunches (lie down like you're going to do normal crunches, but drop your knees down to your right side until they hit the floor, then bring your left knee closer to your chest until your thigh makes a right angle with your torso)
50 left side-crunches (same thing, just switch sides)
50 crunches lying on my back with my legs straight out
levels -- lie down with your legs straight out. lift both legs up to make about a 30 degree angle with the floor, and that's level 1. if they make a 60 degree angle that's level 2, and if they're vertical thats level 3. you only have to hold each level for a second or two, and this is the order i do. 1-2-3-1-2-3-1-2-1-2-1-2-3. do that five times, then hold level 1, then 2, then 3 for about 5 seconds each. then do the long pattern again and you're done. it's a great workout for your lower abs. its hard at the beginning though, so work up the 5x repetition.
if you still have a lot of energy do plank for a minute. you lie down on the floor, then lift yourself on your forearms and toes, and try to keep your body as flat as possible.
word of warning: don't do all of these every day, you'll overwork your muscles and risk an injury.