This website has a lot of workouts laid out so that if you want an idea of what to do, you can grab one and go. The filter at the bottom of the page lets you select the type of workout (abs, strength, HIIT, etc) if you'd like to filter it down.
Total ab work out - really difficult or I'm super out of shape. Good for when I travel
The supposed Bruce Lee ab workout. I would add the "Bruce Lee" level to sets at the bottom, pumping it up to 9 sets. Also a "Beginner" level of 10 reps each for one set.
FITNESS - abs on fire workout Visual Workout Guides for Full Bodyweight, No Equipment Training
ABS - 6 Packs Total Complete no-equipment abs routine with a muscle map.
MasterPack Workout- more abs to catch center lower core