I do the same, ziplock everything with the potential to leak, and double bag serious threats.
Right now my peanut butter is a little Rubbermaid container, that holds about 4 big tablespoons worth. It's probably better for the environment, but I hate the weight and bulk. Wetcanoedogs once showed us refillable tubes that he uses, but I haven't been able to find them around here yet. I've got a little 4oz SAK collapsable flask that I've considered for peanut butter, but getting the PB out of it would be a challenge so it's relegated to holding olive oil instead.
Every time friends and family head South of the border and ask if we'd like them to bring anything back, I ask for Justin's PB packs and SPAM singles because we can't get them here. I'm pretty sure they think I'm kidding because I've had no joy yet.