The Serfas Puck lock is ultra-portable, ultra-secure, and ultra convenient. It weighs in at only 520.9g, so you shouldn't be concerned with the added weight. The chain is 23 inches long, and serves to replace a U-lock or chain as opposed to a longer cable lock.
When closed, it very easily fits into a jersey pocket, waterbottle cage, seat bag, stem bag, etc. If you have many quick release skewers on your bike, you may want to consider getting two!
Check them out at Bumstead's. We'd be happy to show you how one works!