How to seal an outside hole temporarily
As Levi mentioned in a comment, a can of spray foam (urethane) will do the job quickly and easily. It'll last months, at least. I'd use the minimal expansion "window and door" variety to avoid a mess. If you do a careful job that doesn't require shaving lumps later, it'll have a reasonably smooth skin that would probably take paint, too.

Note that urethane foam, caulk, and glue are crazy sticky. They will remain on skin for days and clothing forever. Prepare accordingly.