I find changing weights on the barbells is how I spend the 1 min between sets. The only problem is when someone else in the gym either doesn't remove thier weights, or takes all the plates of a certain weight to one side of the gym and hordes them :P

As for changing your ab rutine, I think regularly alternating exercises is a good thing. It targets muscles in different ways and keeps things from getting boring. Pushups sound great for arms. You might also look at pullups. I started doing some assisted pull ups to finish off my biceps. The stretch it gives the whole body in the hanging position feels great, and if the machine has different bars, you can work different parts of your upper body.