Hooray! Another allotment newbie :)
We got ours 4 weeks ago, it's quite a large plot, and was totally overgrown with grass and weeds. So far we've covered half with weed membrane to rot down til Spring, and we've dug, turned and weeded 2 beds.
We've got swede, beetroot, shallots, carrots, parsnips, sweetcorn and purple sprouting broccoli on the go at the moment. All bunged in together this year, so I'm sure some won't do as well as it should.
We got a shed off ebay and erected that yesterday. We've inherited a large rhubarb plant, some raspberry canes and 4 blackcurrant bushes too.
I've borrowed some books from the library, and have photocopied anything really amazing.
You can get in leeks, winter cabbage, lettuces. If you get some good sized plug plants, you might be able to get in some runner beans, beetroot, sweetcorn. Ask at your local garden centre - they were very helpful to me.
Also get a soil Ph tester kit, as some plants like very acid/akaline soil :)