Forgot your reusable bag? Use plastic!

Pro tip: If you usually bring your own bag but on rare occasions forget... then USE PLASTIC. Don't buy a new cloth bag!  

Cotton tote bags have the equivalent carbon footprint to 327 bags* while tote bags from recycled polypropylene (the kind you see at grocery store checkout counters) require 26* uses. Meaning you would have to reuse that cotton tote 327 times before to offset the carbon cost of just using plastic bags instead. If you go to the grocery store twice a week, that means you would have to use that bag regularly for 3 years!

So once in a while if you forget your reusable bag, it is better to use plastic than to end up stockpiling cloth bags with each of them having a heavy carbon footprint.

This does not mean you should always use plastic bags! Use reusable bags whenever possible. 

^^ This a a non-woven bag made of polypropylene. This is the kind of bag typically sold at grocery store checkouts.

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* There have been various studies looking at the life cycle carbon cost of different types of bags. These figures come from Life cycle assessment of supermarket carrier bags: a review of the bags available in 2006 by The Environment Agency of the UK.