If you have dogs and take bags with you to clean up after them, this would be a perfect answer. I'd keep one of the smaller (square and tall) tissue boxes near the leash. Then pull out a bag when you go for a walk.
Edit to add:
Somebody asked me where to recycle the overflow of plastic bags. I live in the Northwest. Around here, most grocery stores have a container somewhere near the door for clean plastic bags (all kinds- just clean). Every once in a while, I take the overflow with me when I go grocery shopping and pop them in the recycle container. I also pop a few in my reusable shopping bags. When I do my grocery shopping, I pull out my old produce bags rather than taking new ones. But I stress that they are CLEAN bags. I never re-use the ones that were wet inside. Oh- and if you want to save the wet ones, just turn them inside out and leave them on your counter for a while- they'll dry out.
OK- this is MUCH more than you ever wanted to read about plastic bags. I'll stop now. :-)