Budgeting

I am currently working out various things to do with how I'm intending to spend my summer and where I will be when. As part of this I have realised I have no idea if I can afford to go on holiday/go to events; my final loan instalment will be paid in April and May, and then it will be free-fall till the new academic year. Clearly I'll be getting a job or jobs at some point; but I really really need to BUDGET. I need to get a good idea of what I spend on food and so on, so I need to track my spending for a bit *now*, and then when the final batch of money kicks in I need to have a robust and non-fiddly way of keeping track what I have spent and what I have left (plus additional income).

I am not very keen on using prefabricated software for this - I tried KMyMoney and it just has so many categories of rubbish to put things in that I don't understand how it works. I want to make a spreadsheet, I think. Advice, please please, if you have any.