A laptop is probably one of your better options, but you can work out these options with a tablet as well (given it has enough storage and a usb-hdmi adapter). I keep movies on my laptop and give myself a few options.
1. I hook it up to the TV via HDMI and run the audio AUX cable to the stereo in the RV for surroud sound or to use the outdoor speakers (if we're outside watching movies)
2. Just watch it on the laptop and hook up sound to the RV stereo or a bluetooth speaker
3. Just watch it on my laptop with no outside audio options.
This puts most of the work on the laptop, which is easily rechargeable. Granted we always camp with hookups, so power is never really an issue for me, but I do have an inverter if I ever am tailgating and need/want a TV option.
I never rely on streaming options (we have an Amazon Fire Stick) in the RV because it's so rare that we have a solid internet connection that has the bandwidth for streaming. I do have Verizon and the mobile hotspot, but with being inside the trailer and being in spots that rarely have a cell signal, it never seemed worth it to me. Though I have been considering getting a cell signal booster since I work online and it would make internet connections more reliable no matter where I am.
2010 Chevy Tahoe & 2015 Keystone Bullet Premier 30'