I have been down to the plot several times to plan. I may have looked like a very relaxed person sitting drinking tea and reading a book but I assure you inside I was busy thinking and planning. It was quite tiring actually on one occasion I had to come home to have a nap!
The other good thing about taking the time to sit looking out at your plot is you also get to look at your neighbours and get some inspiration as to how you want yours to be. It is important not to get too despondant when doing this. When comparing my overgrown space to that of the other well manintained, organised plots I did feel a little overwhelmed but another cup of tea soon made me feel better.
So maybe my first piece of advice as to what to buy for your allotment is to invest in a good flask. No problem is unsolveable when you can take a step back from it, sit down and have a nice cup of tea.