Update: Lots of people have suggested just plastic bags/sheets and cardboard will do, but not to put them in a loft. Thanks for the help! I've put the whole collection online here to browse through.
Long story short: these belong to my girlfriend's Dad, who stored them gradually in his loft over the last few decades but had to take them down due to insulation work being carried out. There are several large boxes containing many mint condition early/classic Amiga and Commodore 64 games, as well as the computers, accessories, etc. - you name it, it's probably there. Obviously some of the games in the pictures aren't that old or rare, but this only represents about 1/4 of the main haul and I didn't have space to lay everything out. I will try to catalogue everything.
It's hard to tell from the blurry pics but by some quirk of nature they have been preserved almost perfectly in their cardboard boxes. Shop-new in some instances. I don't know if this is a remarkable collection at all, but it is very impressive and would be a shame to sell, so the only alternative is to put them back into storage. I would very much like to know the best way of preserving them so that we can get go on another nostalgia trip in another twenty years. If you have any advice please let me know via twitter. Again, they are in exceptional condition and we would like to keep them that way. Thanks for reading!