Bp's can go off feed for the littlest reasons...
My BP has been off food for over a month now, and it's not the first time! And it's because of the temps being all wackey. If they fluctuate too much or if you don't have a warm enough side.

But give ur snake time, and don't freak out. He/she will eat eventually as long as everything is set correctly. And only try once a week the same day, and try every day or two. That won't help!

I think ur rat died because it was in the pickle jar! LOL... I don't know why you would put him in a pickle jar! Even with holes in the jar lid, you would need a LOT of holes depending on the size of the jar I guess...
I once had like 5 little rats in a little rubbermaid container and I had drilled maybe 10-15 little holes (about the size of a pencil). And they almost died on me too. It was because they didn't have enough ventilation and the humidity levels inside the container went through the roof in less then 12 hours...
I opened the lid and they were all moist and smelly so maybe u didnt have enough ventitlation. But they did live!
Now I use little hamster cages...

anyway, Good Luck with ur snake and your rats!