Like any frugalites worth the title, we wash out our plastic baggies after we use them so we can reuse them again. However, even with this method we can't use them more than three or four times without them popping leaks.
What has worked for me is using plastic containers instead of baggies whenever possible. The containers are marketed as disposable so they're fairly inexpensive, but I've found them to be extremely durable. I've had many of my containers for years and they're holding up just fine even though I put them in the dishwasher and straight from the fridge to the microwave.
They have worked especially well in our lunches. Again, like most frugalites, we pack our own lunches for work. We use the plastic containers for sandwiches and snacks (like craisins), a stainless steel bottle for water, and of course fruit comes in its own packaging. Using all reusable containers we have cut way down on our baggie usage and created virtually trash-free lunches. I love it when environmentalism and frugality meet.