If you think it will be a long time, put ice in a small container, like a tupperware with
lid. Then wrap the container in layers of newspaper, which acts as very good insulation.
If you run out of ice, you might have snow outside which can be used.
Do not let the vial directly touch the ice or snow.
Sometimes, you can put things outside, if the temp is above freezing but below about
45-degrees. In the shade only, not in direct sunlight.
I always keep a few of those small blue-ice packs in the freezer. You can quickly
set up a temporary small ice chest with those.
It's good to have a freezer thermometer that you can put inside to check the temp.