Put some thick oil (ie: Phil Wood's) in your lock's key hole to prevent it from freeze in the winter. I've learn that one the hard way. Lock de-icer (which I had to go to three gas stations to find the middle of the winter) didn't work. I had to resolve to using my lighter (thank FSM I'm a smoker!) to get the ice inside the lock to melt. I now carry around a small butane torch. It then happened once more, but that time I was prepared. But since having added some oil, I've had no other freeze.
Carry around a bunch of tie-wraps, it'll hold many things and even replace bolts & nuts while you get home/to the hardware store/lbs, comes in one (or two) size fits all and weights less than their value in cash at the dollar store.
Straps holds things on a rack better than bungee-cords.
If you've just reinstalled your seat after having locked your bike, and realized a couple of blocks afterwards that it's not straight, you can usually straighten it by grabbing the seat with your thighs, unclipping the quick release, repositioning and re-clipping. Make sure you have a fair stretch in front of you!