You need:
This is almost embarrasingly easy – it comes in strips that push in between the wall uprights and stay there because they’re just a fraction wider than the gaps between the beams:
The only tricky part is that the wall isn’t quite twice as long as the bits of insulation, so I had to trim every second one down to size to get it to fit nicely:
All done:
This is also pretty easy – it comes in a big roll that’s a bit wider than the wall is high, so you just unroll it and staple it up. The only tricky part is making sure it goes on straight, because the top of the uprights is 8 feet up which is a little bit awkward to hold plastic against, it keeps on wanting to fall down.
This was trickier to do:
Here’s another view, and also the second wall of the garage that got insulated: