You can still buy portable DVD players with a laptop-sized screen, with composite in.

Other than that, you can buy relatively inexpensive converter boxes that take composite video and analog audio, and output HDMI.

A USB video capture device or a converter box. There are devices sold specifically to interface these old machines with modern displays. One of the more famous ones is the RetroTINK.

I'm using a Pelco 9" PVM that had a former life as a security camera monitor. Suprisingly good video for composite, but alas its not very large.