I use a good half inch, self-coiling combination cable lock. I think it is the OnGuard brand. I find it is convenient.

Cables are a pain to cut with handheld wire cutters, but there are cable cutters about 3 feet long that could do them in. Just like 3 foot long bolt cutters, except that a bolt cutter won't cut the cables easily.

Anyway, it depends a little bit on the bike. Is it a $100, $500, or $5000 bike?

The cable lock should be fine for a brief stop in a store with a mid-level bike.

The story is that my impenetrable U-Locks can be defeated in a matter of seconds with a simple 50 cent Bic pen.