This was my first thought, yeah.
But seriously, I don't know that there are games expensive enough for me to be able to spend 1m in a day. If you can't include payments for a house big enough to actually fit an awesome gaming room, then I'm not gonna fit all that in my tiny flat at all. Not even close. So basically I'd end up having to donate whatever I have left after my initial purchases to Child's Play.
I mean, I legit am not sure I could actually go through that many purchases on various sites/shops in a single day. It'd be so crappy.
If I'm allowed to buy a sweet house to put all my games and gaming stuff inside, then I would absolutely buy a sweet house first, buy some awesome amazing PC rigs and large numbers of monitors, TVs, consoles and controllers, couches and chairs, and basically make a place that just screams "everyone come over to my place we will game all day everyday". And then I can either rent it out or I can actually make use of it.
Leftover cash, again, Child's Play for sure.
Bow before the mighty Javoo!
I'll give you the easiest way to spend this money and not lose it:
If you own a house, this is easier, if you own land with the rights to develop on it even better. If you have a den building on your land then fantastic. If not, you could run in to some troubles but it could be done:
Build the ultimate gaming den, in your home, if you have the land with the option to develop on it, simply paying for the development of your den would eat up hundreds and hundreds of thousands of pounds. Sure the "den" wouldn't be finished before the 24 hours, but if you pay for it you're sorted the rule said spend the money, not that I couldn't spend it on trout that will take me time to get done. You want super fast fibre connections? Sure have them piped in for another 20 - 50 grand, build that super powerful PC you dreamed of, get the best TV you can find, a PS4, Xbox 1 and hire some dudes on minimum wage to make the purchases for digital content you want on them because heaven knows you have the cash for it. Kit that den out in the most luxurious seating/flooring/desk you want. have hard-drives installed in the walls go smurfing nuts.
If after doing all that, you still have money left over, you could probably buy the rights to some smaller studios that are developing interesting things, or you could simply blast ten thousand pound a time on various kickstarter game campaigns that you like, twitch streamers or whatever, you go smurfing crazy and spend spend spend.
If you can't spend a million quid doing that, then you're doing it wrong.
Think a couple of microtranscations will finish it up in less than a day.