I use the three packs of Baby bottle warmers that can be found at Wegmans. They are usually around $2 and they last quite some time. Just throwing them in the microwave works great.
On a different note, I buy Rico's buttering toppering, which Cinemark uses. I placed an order with them last year for one gallon but they sent me four of them, for the price of one. The next day they changed their checkout system so you had to order in bulk. 12 salt packages or 4 gallons of butter at a time.
I have two things of butter left still and was wondering if anyone knows how long this stuff is good for if it sits on the shelf?