A small portable scanner. I don't take it anywhere I just got a portable one due to it's size so I can stick it in a drawer.
I've been able to save a bunch of space and get rid of 99% of documents in my filing cabinet by making a digital copy and getting rid of the physical ones. Now when I get an important document I scan it save it to a few places and get rid of it.
Why not just a scanner app for your phone? They work pretty well. I have a flatbed scanner that I keep stored away most of the time, until I need to scan a bunch of stuff quickly. If I need to scan the odd receipt, I use Tiny Scanner.
The main reason was I had 2 filing cabinet drawers filled with paper and wanted something that could be relatively hands off. I was able to do double sided paper and load multiple pages at a time (24 pages before it didn't work well) so it was easy to burn through the them. I've tried a scanner app before for one off things and have had okay success with them. I guess now the backlog is burned down I can compare the two for things that are just a couple of pages.
I ended up getting the Canon imageFORMULA R10 off of amazon but there are a few similar options. Does double sided scanning and I was able to load 24 pages at a time.