Dave is right on - dry ice won't give you the
effect you're after, plus it's a PITA to deal with - in solid form it has to be handled very carefully, you need to have proper storage, you have to get it delivered every couple of days as it sublimes away quite fast and it involves using hot water to get the
effect. You'd be much better off with a small
smoke machine; there are loads of relatively cheap "disco"
smoke machines available; when they're on the heating cycle you can't get
smoke out of them, unlike proper theatrical
smoke machines which will pump
smoke all the time, but in your case it shouldn't matter. Unless you get a battery powered one (we have one which was bought for Beauty and the Beast to go in Mrs Potts' costume!) you are going to have to run a
power cable and remote control cable to the trash can. There are a few different battery powered ones out there - talk to your local hire company - but they do tend to be fairly small. That may suit your purpose though, as I guess you don't want clouds and clouds of
smoke pouring out of the trash can!