For serious authentication purposes, especially if you collect oddball items and ephemera (posters, booklets, signs, trade cards, prints etc), a microscope is important. I think I wrote 100X, but 60X likely is good too. You can buy inexpensive handheld ones with light one eBay and amazon for cheap. I'm not endorsing the seller, but the below link is to an example one. It's lightweight and portable, you can carry it with you wherever you go.
https://www.amazon.com/Carson-60X-10...ble+microscope
The below link is to a digital one that plugs into your laptop. It isn't portable (unless you count taking your laptop with you as portable), but you can see the microscopic images on your computer screen and take microscopic photos. I've had collectors take microscopic photos and send them to me via email which makes it easy on my for giving authenticity opinions. Plus it's pretty cool and fun to take microscopic images. If you have kids, it's great for them too.
https://www.amazon.com/Portable-Micr...ble+microscope
But for normal collecting purposes that cheapo in the first link is fine and dandy.
If you get into old photography, such microscopes are great for authenticating 1800s photos.