Yes it is, to continue working on the other computer you would have to have the same software program to do that. But the other system could be a brick and your USB stick isn't going to change that.
Yes you would have copies of some files, but you have to select those files and back them up regularly to the USB stick, you could get caught out.
As I said I do a weekly drive image of my system, I also run a little batch program (at least once) daily for all volatile files that are likely to change frequently, documents, images, emails, bookmarks, etc. and save those to another drive, that could well be to a USB Stick.
You have to have a backup plan (whatever that is going to be), fail to plan then you plan to fail.