Lost usb with wallet backups
If someone finds your USB and it has a full backup, they’ll be able to recreate your current wallets and steal all the funds. If you still have a working instance of those wallets, then you should immediately transfer all funds out of them and into new wallets. Do not use the original wallets to store funds ever again, create a brand new wallet (ie new seed) and use that from now on. 

Be careful with your backups, if someone stole your coins you would likely have no recourse at this point.