A high strength Kensington MicroSaver Lock and Security Cable will make you feel more secure when you leave your laptop unattended.
The MicroSaver uses a patented T-Lock to attach to the security slot which is provided in most high quality modern laptops. The cable is 6 feet long.
Even if you can't find a suitable permanently fixed object to lock to, you can usually find something large (such as a chair or desk drawer) that a thief would feel self conscious carrying away with your computer. I make sure that my laptop is locked if I leave it during lunch in an unsecured office. I lock my laptop in the trunk of my car if I go to the shopping center or out to dinner after work.
In reality, the MicroSaver will only slow down a determined thief. If he (sorry if I am being sexist) has a large pair of bolt cutters then forget it. Also, I am not sure if it is a hoax or not, but there are videos on the web of people opening Kensington locks with a hack using the cardboard from a toilet paper roll. So, if somebody comes across my secured laptop, I hope they have neither bolt cutters or a roll of toilet paper with them.
I am quite happy with my Kensington MicroSaver Lock and Security Cable. They make me feel more secure.