Marché d'Aligre
The cheapest open air market in Paris, on Rue d'Aligre. There's produce, carpets, clothes, antiques. Covered market, Marche Beauvau, is adjacent. North African influence, many food shops surround it.
New PC Charenton
This is just one example out of the many computer shops in the immediate area, included here to help you find them all. Check the prices here, next door, and across the street. When you find the lowest bidder plunge forward and add them here please!
A Carnaval & Fetes
Cyclades Electronique
A cut above the others, and on the other side of the station, Cyclades is the place to go if you need parts. Perhaps you have an out-of-production laptop which needs exactly 18.5 volts? They've got the charger. They've also got a full range of capacitors, resistors, transistors, chips, model airplane electronics and mechanics, tools, and much much more.
Foire du trône
During the spring time there is a carnival called the Foire du trône held in the Bois de Vincennes
There are any number of shops catering to the needs of travellers in and around Gare de Lyon, where you can easily replace a piece of broken luggage or even buy a suit if you suddenly find yourself with a business appointment.
The archways of the former railroad right-of-way which now support the promenade plantée are home to trendy restaurants, designer's studios, and art galleries. Taken as a whole it's known as the Viaduc des Arts', and is well worth a stroll for those interested in art and design.
Another shopping highlight of the 12th is the amazing number of electronics and computer shops, mostly clustered around rue Charenton near the Jardin de Reuilly, as one would expect the intense competition keeps prices low for Europe.