How do I make this awesome plastic cauldron safe for serving drinks?

You could get one of the http://www.reynoldskitchens.com/products/slow-cooker-liners/ that are made to line slow cookers or a http://www.reynoldskitchens.com/whats-new/whats-new-items/oven-bag-roasted-turkey/.

I have the same cauldron. Mine also has a small hole in the bottom. For Halloween last year, I went outside and found a bunch of sticks, and lined the inner rim of the bowl with them, so that they were "sticking" up. It looked cool because....you know. Witches fill their cauldrons with sticks ;) It was sort of nest-like. And then I put a black plastic bowl inside of it. I found the black plastic bowl at the dollar store. It really looked cool. I also had a big plastic bone, and used that to stir the punch. No one died.

http://www.dap.com/product_details.aspx?BrandID=67&SubcatID=27 is food safe. Happy Hallowe'en!

If your regular punchbowl is too small to fill up the cauldron, maybe you could go to a party supply store* and get a bigger, clear plastic punchbowl that DOES fill up the bottom of the cauldron just for the occasion. I'd put a piece of dark cloth under the bowl inside the cauldron, and then set the cauldron on a place mat, just in case any leaks or drips work their way out though the hole in the bottom. *they may even have something appropriate at the grocery store or Target/KMart/Wal-Mart at this time of year.

You can check the number on the bottom of the item and cross reference to http://www.dap.com/docs/msds/00000688_english.pdf for safety. As for sealing, I like the chocolate idea, and although that silicone adhesive claims to be food safe, I'm not sure I'd go there looking at the .

Fill it with packing foam peanuts and dry ice and then put the regular punchbowl inside. That way you're sure that it's safe to serve from, and it stays insulated and cool with creepy Halloween fog, and doesn't sink too far inside as the dry ice evaporates. If dry ice is a problem, just use the foam packing peanuts.

Could you carefully line it with a few overlapping layers of plastic wrap? You'd want to tape it or something to the underside of that little ridge around the opening to avoid it flopping down while in use.

I am not a cauldron expert, but my honest feeling is that it will be very difficult to come up with a cheap, easy, and satisfactory solution other than using your regular punchbowl inside, as phunniemee says. You could use sand or something underneath the bottom and edges of the regular bowl so it fits nicely before adding dry ice round the top (or ivy or other spooky stuff if you can't get dry ice?)

Could you coat the inside with thick Jello (or just regular gelatine)? Use less water than usual, then paint it on. Not sure if it would dissolve with the alcohol. Maybe try coating it with caramel made by boiling down sugar. Paint it on the inside. If your punch is cold and sweet, it may not change the taste that much. If it's not a thick layer of caramel, it's likely to crack.