Basically this: https://voltaicsystems.com/arc20w-kit/. It's a bit on the expensive side, I'm sure you can find cheaper kits. I like that the battery has a USB-C port, so I can charge the MacBook directly. To be truly off-grid, you need something bigger though. 20W is ok for basic work, but if you're compiling or doing other heavy work you need more power. If it's a bit cloudy then the battery won't fully charge with that panel, I'd recommend at least 50-100W. But with that size you're also less mobile. I had a car so mobility wasn't that important for me. The only important thing for me is that I can take the gear onto an airplane when traveling.

I need to investigate if USB-C car charger adapters can charge a MacBook. When traveling with a car and the sun doesn't shine, it would be a nice backup solution. I was basically living in a car + tent for four weeks, traveling and working.

I do similar with gear from https://GoalZero.com, typically using a car-portable 100W panel + 100Wh battery with USB-C support when seriously traveling, and a briefcase-friendly 20W folding panel + same battery when mobile. Wait for specials at https://REI.com to get good prices.