I have stashed bags in train and bus station luggage lockers and storage rooms all over, and I’d suggest you not worry that much. The biggest problem I encountered was forgetting how to find my locker again in huge train stations like Osaka. The bus terminal in Riga was delightful in that respect: I think there were maybe 15 lockers total.
Make sure you have a small day bag with essentials (not just wallet and documents, but meds, phone, etc.) that are difficult/impossible to replace on the road. Take that with you, and leave the bulk of your stuff behind. I’d guess you could fit your Surface into the day bag too, so that’s not left in the locker.
In the unlikely event something does happen to your stored bag, it’s critical to have travel insurance that covers luggage theft (and I’d double check the fine print on theft from lockers to be safe). That way, you can replace the clothes, toiletries, whatever and carry on with your trip.
At the end of the day, stuff is stuff, and it’s much less valuable than time, because you can’t replace time.
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