Hi bamboo, I've never tried growing spuds in a bag, do you make your own compost? Suds always manage to pop up in my compost heap!

I suggest you try for a salad type spud. Garden centres will have lots of types to choose from, and they display general info about them.

You probably won't have to worry about the different types of potato and go for a good cropping first early.
Try to get them soon because you will have to " chit" them be four planting. I sit mine in an old egg box on a window sill. Rubb off all but 2 of the eyes on each spud leave the ones that look the biggest. They will begin to sprout. Plant after a few weeks ( don't let the shoots get too leggy.) These get planted so the sprouts will form the crown.

Don't forget to keep watered as I guess they will dry out fairly quickly being in a bag.
When the crowns of leaves appear, cover with compost. That will encourage more growth and more tubers, that means more beautiful home grown spuds.
Happy growing.

I agree with all Thechickenlady above says and thanks for a few good pieces of advice too.
I did a few bags one year - they were OK, but don't put more that two potatoes into each bag as there's not so much space in there!
The only other disavantage is that when you come to harvesting you have to more or less empty the whole bag out and use all of what's there. Unlike a proper bed where you can choose how many you want to dig up at a time.
I would diffinitely choose 'speciality' salade varieies, e.g. anya, fir apple, etc as main crops take up so much room and it's just not worth all the effort, in a small bag.
Good luck!
Anne