Never had a problem myself there both GA and commercial.
If you do go back if you pay at the big C just under the tower then exit the terminal turn left as you come out and with in 5 mins walk there is one of those Brewers Fayres that do the pub grub. If you want a longer walk turn right and walk down the road past the playing fields and you will come to a food stop that does takeaway from a old railway carrage or sit down overlooking the railway bridge and Tay.
There is a half decent coffee shop in the ground side bit of the terminal. The flying club has a couple of machines for snacks but nothing special.
If you want to go into town its about 8 quid in a taxi or there is a bus that goes from outside the terminal.
Dundee I have a soft spot for. Spent many an hour waiting for a 50hour check to be done and also on diverts when the wx in Aberdeen is pants.
Yes the firemen are multi tasking and they will go and do the very few commercials first. Its revenue!!! If Dundee did shut it would be a right pain in the bum for GA. Its the only cheap airport on the east coast where you can get fuel from 6:30am until late at night when the likes of CUM and Perth have shut up shop.
Security are friendly, greet you with a smile and if one is given back make the whole proccess a none event unlike some other commercial airports with GA. Although I must admit most of the regional airports in scotland this applies to.