I buy these at my nearby Home Depot (A box at a time, not by the pallet):

http://www.homedepot.com/h_d1/N-5yc1vZ1x...catalogId=10053

I use them in the yard to bag leaves and they do not weigh much when put in a kit. I understand that they are only 1 mil and you want 3-4 mil but I have no complaints. Have used them a little backpacking and hunting with good results but never in what I'd call a survival situation.