I know it's already been said, but those "U-Locks" weigh a TON! The big Kryptonite ones marketed for motorcycles are especially heavy. I'm no weany, but I NEVER carry locks or chains if I can help it...leave 'em on site...get several, one for home or the gym.

Another college tip...don't carry shoes if you can help it (very heavy and bulky)...I left a pair of Tevas locked up to the racks with my U-Lock, with the lot covered with a plastic bag....for a WHOLE SEMESTER. Nothing bad happened to them.

Don't carry a proper towel either...those 'Sports Chamois' are much lighter/more compact and are excellent for drying off if you can access a shower.

Also, I found a cheapo chain and padlock handy for locking up my helmet and front tyre to the bike frame or the racks....I used the U-Lock to secure the frame and rear wheel to the rack. Sounds complicated but is quicker/easier and means the bike is more stable being left 'fully assembled' with the front wheel still in....harder for idiots with old clunker bikes to knock yours over or push it to the side. You don't want to carry your helmet around with you all day either.

Also, a CO2 bottle tyre inflater can be a little tricky if you're not familiar with them, but is another worthwhile space and weight saver over a pump for commuting.

Finally, I must admit, after years of the above, I want a (another) motorcycle for commuting. I'm sorry, but I do. They're a bit more expensive tho....sigh.