I nicked the idea from FB - including the idea to do it backwards - so can't really take credit :o
I sympathise with the Christmas spend total. I am really glad I kept my spreadsheet this (erm, last!) year, as I'd stuck my head in the sand on previous years, but oh boy was it a shock.
I've already set up a much more detailed spreadsheet and documents for next (erm, this!) year. The main thing that should help is that I've made a note of all the other people that need a present, including a few December family birthdays like my great-nephew. In the past I've solely focused on my DH, DSCs and DCs, as I LOVE finding presents for them, and ended up panic buying for everyone else at the last minute which ends up stressful and expensive. Now I've got a table with all the other people and spaces to write what we get them. I did manage to do most of it earlier this year and it really helped.
Also, I've written a list of 'categories' for the DCs' presents. Can't lie, I do buy them too much, even though I've cut down a little year on year. On Christmas day the only presents are chosen by us, as my parents and Grandma give us money to choose something. I go a bit crazy choosing things! So this year I'm planning (planning!) on sticking to the table, I've even got one for stockings e.g. one book, one cuddly etc, so that I know they'll get a good range of things to see them through the year, but it won't be an endless pile of stuff.
I also need to budget for the fact they will need clothes. I was trying to deny it but TBH now they are home ed they wear things out faster due to not wearing uniform 5 days a week! So that added a lot to the overall spend despite mainly sticking to places like Asda. Anyway, they really loved getting clothes as a present so I've written that on the list and I can look out for sales earlier. We've agreed that they can choose (again in supermarkets etc) if they need a few bits in summer, but at Christmas they are happy for me to choose.
Sorry that waffle was epic.