For a GBC pack:
I think I’d put one of the GB Game and Watch gallary 3 in there. They are actually pretty fun. I got hours of entertainment out of them. Kinda wish nintendo brought those back because the redesigned ones were really good and the NDS/3DS would have been perfect to bring back the dual screen Game and Watch games, alas. (edit, they did make them for the NDS but they were club nintendo exclusives or something!)
I think I’d also stick Legend of Zelda: Oracle of Seasons/Ages despite not finishing it? I guess. It was one of the last GBC games made by a first party team. It looks great. It should probably be in there!
Last is a bit of a stupid curveball but Wacky Racers for the GBC was made by a bunch of british demoscene people and actually looks pretty good. I have no idea if it actually is good, other than a demonstration of the hardware. Wacky Racers is a weird title to adapt.