What you guys can do for fitness is look up the USMC PFT Standards and try to get as close to 300 as you possibly can (minus the pullups - Navy doesn't need those). That way you can CRUSH at OCS.
I've been doing a lot of different running programs and a very simple plank program that have absolutely benefitted my overall physical fitness.
For planks - Just keep doing them. Do sets if you have to, but get at least five minutes worth of planks every day.
For pushups - Just keep doing them. Aim at least for 100 good ones a day.
For running - Sprints are great!! But also look up some 5K or LSD (Long/Slow/Distance) programs so you can mix them up with sprints throughout the week. Look up the Manchester United Runs - y'all will love them! Fartlek runs are great too. Bonus points if you run on hills! Just keep doing them.
Honorable mention - Get a foam roller, stretch, and do yoga so you don't f*ck up your legs!