Can you take a thermos on a plane and if so, are there any restrictions or guidelines to follow"?

Yes, you can take a thermos on a plane. However, there are restrictions on the contents of the thermos. Liquids must be in containers of 3.4 ounces or less and all containers must fit in a single quart-sized plastic bag. Additionally, the thermos should be empty when going through security and can be filled after passing through.