Once I understood that presents came from my parents (which I did while still young, given that my parents never bothered to hide it overmuch, so probably around 5-6), we used to enter into a discussion quite early in the year as to that years' present-budget, to be subsequently divided as I saw fit between my birthday at the end of summer, and Christmas (I usually preferred to back-load it 2:1 towards Christmas, though in hindsight, this may not have been the shrewdest way to split it). The total would be dependent on what I got the previous year, though I learnt the benefits of indexation and other cost-of-living adjustments very, very quickly!
Once the total was agreed upon, I could start determing what presents I wanted and then put the contract out to tender (also known as telling mum which shops to call to see if it was available and at what price...

).