said by Monkey344 :
the water in your p.traps for sinks and tubs will eventually evaporate. Therefore you may want to get some of those rubber plugs. Else the sewer gases might come up and leave you with unpleasant odors.
Good call - also, pouring a little mineral oil (not vegetable or animal-based oils, they'll go rancid) down the drains will help prevent the trap drying out... Doesn't have to be much, less then 1/4 cup per drain should be lots.