Fish oil is actually mostly saturated fat -- but its rich in Omega-3s, which is good.

Does your food hall have Olive Oil in a bottle at the salad bar?  I suggest taking a tupperware and filling it with the olive oil and taking it back to your room.

Put olive oil on everything man. Saturate your food with it if necessary.  Makes veggies taste delicious and will get your calories up way high.

Fruit juice post workout is better than just hangin out...so it seems like you're def on the right track there.

Oh, and btw, make sure you lift heavy things ... without aggravating your back

Military press is fine -- but you would need to be careful to stand upright with your back problems..i am sure you would feel a twinge and could bail at the first sign of pain though...make sure you do these standing, too, btw...

Squat is good, but DL is king for mass gains.  Squat will make you stronger than an ox, for sure, but DL is pretty damn damaging (in a good way.)

I would DL conservatively...and maybe even squat with very light weight and strict adherence to form.  Squats with a weight vest would be good too at high speeds.

Bench u can ask some dude around u to spot you -- believe me, it helps...a TON.  Make sure not to arch your back on the push off as this might aggravate your back.

Weighted Pullups and Dips will be the easiest thing for you to do safely -- and they can be pretty damn damaging themselves, which will cause growth.

I recommend a routine pretty heavy on weighted pulls, dips and DLs with a strict aherence to form.  for OH pressing ability, the military press is good, standing, as are full ROM HSPU on parallettes.  Planche will likely be better for you in every way than benching...work on planche pushups (Pseudo Planche PU, Tuck Planche PU, Straddle Planch PU, One leg planche PU etc.).

Also, lever work is pretty damn intense too as well as one armed chin work.  OAC Negatives are a great way to start, as are assisted OAC pullups (using 1 finger or something like that).  Tuck Front lever pulls and pullups are very intense and will definitely make you bigger.

Also, don't forget Sprints...great for developing the lower body as a body-weight-only exercise that will keep scaling with intensity naturally as you get faster...and should be just fine for your back.

Ugh I really wish I could do sprints but I can't.  I don't know about weighted pistols I'll give them a shot today.