While a lot of attention has been given to single-use plastic grocery bags in recent years, little zip-lock bags share all of the same problems that shopping bags do: almost always used once and thrown away, rarely recycled, petroleum based, non-biodegradable, plastic bags make up the majority of ocean pollution.
On the other hand, its a good idea to bring your own lunch, which saves a lot of money over eating out every day.
Its easy to find a cloth bag, mini-cooler, or lunch box to carry the complete meal in, but you still need something to keep your sandwich from falling apart inside your lunch box.
You could wash out and reuse the same ziplock bag over and over, but they aren't easy to wash or dry, and they aren't that durable.
A few companies are selling reusable sandwich holders, but they cost $10 or more.
You can make your own for free in just a few minutes!
-a big piece of paper (an unfolded paper bag works)
-a 16" x 16" (or bigger) piece of strong plastic film
-a 16" x 16" (or bigger) piece of cloth
-pencil or pen and chalk or marker
-a sewing machine or needle and thread
-velcro (could substitute a snap, button, or other fastener)