You still need to charge that pen drive through a USB port. So with which intervals do you need to charge the pan drive? And for how long? And the WiFi on it...how secure is that? (WPA-2 or better?)
Look, it is always the same. Convenience == insecurity. And it always means that the information is not that important after all. Maybe in the mind of the owner, but not in reality. If they are so afraid about information being lost when the laptop is stolen...the cloud isn't going to help you. Especially when the laptop is your only computer.
After all, how long would it take for the thieves to retrieve passwords to online services? If they set their minds to it, not long. Oh...you used a password manager. How nice for you. The delinquents have this software on your laptop. How long before the master password is revealed? Again, not long.
If you want to have a backup, you must disconnect that information from the device you create/edit it on. Because if you don't, the backed up information info is just as susceptible to thievery, in-house accidents (water or fire damage), malware and/or viruses as the original information. You might have the impression that you have a backup, but, in reality, you won't.
Sorry to burst your bubble, but when the occasionally connecting of pen drives is already too inconvenient...don't even bother with backups at all. Maybe a bit harsh, but better this than finding out the really hard way you don't have a backup and lost whatever 'extremely important information' you had. Backups have nothing to do with convenience and much(!) more with discipline and it really would be better if you realize this sooner than later.