I would travel with it to a remote destination s as far away as possible and hand it in to the police. Wait 30 days and collect it.
TL; DR Definitely not keep it, not even remotely worth it. Once when I was working in conveyancing a client wrote a cheque (yes we used cheques back then) for the value of 70% of the property they were buying and I said "make it out to the name on the card" meaning the firms name - we needed the money in our accounts to be able to pass to the sellers solicitors. They put my name on the cheaue rather than the firms name and I didn't initially notice (for about 5 mins) and was holding a cheque made out to me for around £350k. Obviously I told them of their mistake and they tore it up and wrote a new cheque with the correct information. For me to run away with the money - and give up on a lifetime of earning actual money and living my life as I had originally planned - it would have had to be about 10 times that. Even then, realistically, you're not going to end up being able to keep it. There's a million things that can go wrong and the hassle isn't worth it.
I'd swap it into another suitcase as soon as possible and saunter off with it. Then work out a variety of schemes of converting it into a currency that is useful to me over an extended period of time.
Hand it in tbh, that amount of money would have some trackers in it and hit men would be on to you in a flash.
