I use a combination of mini files and sanding blocks.
This kind of thing: https://www.amazon.com/Mangocore-10p...ateway&sr=8-13
https://www.amazon.com/Sackorange-Di...ateway&sr=8-13

Also have a couple big files.

The other thing to look at is wood turners sanding cloth. https://www.amazon.com/Assorted-Abra...gateway&sr=8-4

I have yet to bring my sanding cloth up from my wood working shed to the 3d printer workshop.
The cloth is a lot more amenable to being wrapped and made into different shapes. Normal sandpaper tends to break up when you try and mould it.

A trip to your local buckstore or hardware store is in order :-)