Wasn’t there someone who accidentally threw out a hard drive containing hundreds of bitcoins? If you know when he did that, you might be able to intercept the trash on its way to the landfill.
Here’s an idea if the time-travel is a one-shot rather than a lather-rinse-repeat. Take back some sea salt to Roman times and trade it for some silphium including the seeds. Bury some of the silphium in an urn saying “Noli silphium meum tangere” On an Italian vacation you discover the urn and start growing silphium with you. Note, you brought the seeds back in your time machine so they are viable and genetically they match what everyone agrees is real silphium.
He actually went to the landfill trying to find his old hard drive. He never did.
Stephen King has his lead character trying to do this in 11/22/63. Despite not placing his big bet twice in the same place, word gets around among the underworld types he places his bets through, and they come after him and almost fatally beat him up (they don’t know how he could make such uncannily good predictions, but they don’t care. Not only don’t they want to keep him from doing it again, but their pride was hurt.)
Safer to memorize stock futures and play the legitimate market.
Yeah I forgot until recently sports betting in the US meant going to a sketchy guy at a bar, that seems like a good way for a time traveller to get beaten to death
I was talking about actual legitimate gambling companies. I can got to the sports book in Vegas right now and put down a series of bets that will make me a billionaire or trillionaire (pretty easily done), would they take that bet? As a non-time traveller the chances of winning are infinitesimally small but not zero, can they take the bet knowing they would not be able to pay me if I win. What happens if I win? Would they be legally obliged to close down the company, and sell everything to pay me as much as they could?
Or just buy them when they were <$100
I remember a short story where the past was immutable so the protagonist could not put a lot of money into the market because that would change the quotes. Similarly horse races since that would change the odds.
The Powerball jackpot on Monday was $1.2B with no winner. Go back in time three days, play the winning numbers, don’t even bother returning to the present via the time machine, just grab a hotel for a couple nights and avoid running into your past self.
Or if you’re greedy, wait to see if there’s a winner on Wednesday and perhaps grab an even larger jackpot.
But you’ve altered the timeline so that there is/was a winner for the Monday’s jackpot. Your past self notes that somebody won, has no idea it’s their own self, so doesn’t go back in time. Now there’s two of you running around. I guess 1.2 billion is plenty to share with your other self, and all that money can go a long ways to allowing both of you to exist with the same set of identity documents. 
Not an insurmountable problem, but what am I buying them with? I can probably source enough pre-2010 bills, but I need to get that money into the financial system so I can swap it for the Bitcoins. Plus, mining should be cheaper, although that is a minor consideration.
But that brings up a thought on this:
What am I buying a 2010 machine with? 15 or so years isn’t a huge problem in sourcing time appropriate cash, but a stack of 2025 $100 bills is going to look like counterfeit money.