I've only had my allotment a year, so I think guru is a bit optimistic! 
I'd do potatoes in sacks. We currently have our second batch going to keep us in spuds through winter.
Peas and beans tend to be quite easy. Carrots depend on your soil type; they don't like heavy soil. You can sow broad beans at the end of next month to overwinter, as well as peas like Early Onward.
Sweetcorn can be fussy (I soak the seeds for about an hour before sowing them), but is very tasty and easy once they're on the go!
We seem to be doing well with pumpkins and squash.
Our alliums (onions, garlic and leeks) didn't do amazingly well this year. I'll try once more then give up, I think!
My brassicas are OK, but take up too much space for very little reward.
Lettuce and beetroot have been hit and miss for me too.
Courgette and cucumber are OK. And my tomatoes are just coming good.