I remember spending 2 days at one shop improving his 'front window' once, he told me later people were popping in to see who the new owner was ...
Well, you have covered one aspect of the business that needs addressing PDQ, the shop front ... if as shabby as you describe then that is not going to ensue confidence to buy a PC from, now is it.
Gadgets are a little on the niche market although Ipods are "fashionable you won't get them to sell unless you opt for the 'grey' market and or get cheap knock-offs.
Consumeables is what you need ... Ink refilling services and compatibles inks can be an asset to get people into the shop, cheap peripherals such as Printer cables ... I know how much they cost, I used to give them away, and I know how much you are going to be charged at PCWorld for one ...
Free inspections, "if we don't fix, we don't charge" it gets them into the door and if you can "look at it while they wait" even better AND even better, do it in front of them ... have a small "inspection" area where you can plug it in and let them watch, be prepared for a lot of questions though ... shop browsing while waiting can sometimes make a sale.
I never "needed" any 'stock' in my workshop as I could get anything I needed next day, I had loads of posters though ... and I always said it takes 3 days to build a PC

allowing me time for DAOs and other unforseen problems. However, I always offered the latest 'computer gizmo' on the market, you don't necessary need an M2 PC in stock to sell one.
I never advertised either, but it did take a year or two to build up a reputation as a good systems builder ... one drawback is my PCs would easily last you 3 years, but was always pleased to see old customers returning for advice and a new system. Never ceased to amaze me how many phone calls I got from people stating "a friend of mine recommended you" ... nice feeling that.
... now I'm rabbiting.