10. He Doesn't Need To Exercise
As is helpfully revealed in the Official Handbook of the Marvel Universe, it turns out that Captain America's super-soldier serum is capable of continually keeping Steve Roger's body at peak condition, meaning that Cap could have been eating junk food all day and still have maintained the same level of durability and super-strength he's renowned for.
This makes it doubly impressive that Steve still puts the effort he does into exercise, as it's clearly motivated by wanting to stay disciplined, instead of needing to keep up his physical fitness. Given he's explicitly told he doesn't need to keep working out in Captain America #384, there's been plenty of time for the hero to give up on his health regime, but the fact he hasn't clearly shows the level of commitment America's Hero puts into every aspect of his life, necessary or not.
While it's funny to think of Steve using this as an excuse chow down on some pizza, it also serves to explain why in storylines where he's been kidnapped or malnourished, the hero is still at peak form - which is less amusing than the junk food stuff, but also entirely more important.