Jordan Ellis sews a variety of nerdy aprons for men, women, and children, many of which can double as costumes. OK, maybe you wouldn't wear these to Comic-Con, but they're still fantastic for impromptu LARPing. Possibly also that cooking thing.
Tardis Apron
Source: etsy.com
Powerpuff Girls
Source: etsy.com
Spider-Man Apron
Source: etsy.com
A close up of the Spider-Man insignia and the fabric.
Source: etsy.com