Hunting & Fishing Half vest / sitting equipment

[threetrees]

I'm looking for something like the cabelas half vest. however, i do not need the side pockets.

ideally, it would be only a flat bag, i fill it with a thick insulation mat (of appropriate size) and slide my belt through ...

yes, i do not want to unpack my backpack, nor do i want to carry something in my hands. it should be a simple - 'sit down and have a dry/warm bottom'

any recommendations? what do you guys use?. thanks for your input