Wooden spoons, great for spanking
Clothespegs (also wooden) make for good impromptu nipple clamps, and can go elsewhere too.
Rope is actually surprisingly innocuous, just tell people you have it for camping or something of the sort.
Candles are a good one- you've probably got some already, just in case of blackouts.

I'd also recommend doing a search on the site for 'pervertibles', which is the general name for things like the above- every day objects that can be re-tasked to kinky uses.