For Tamagotchi V1 - V5 you keep all your gotchi points and the food and items
For Tamagotchi V3 and V4 or V4.5 you will loose your souvenirs but you can enter it again in the next generation
For the first edition of Music Stars, you will keep all your Gotchi points, items and food and awards
For the second or later edition of Music Star, you don't keep any Gotchi points, so you start from 0 Gotchi points again. But during their childhood or their teen lives, nazotchi will come with some of the gotchi points the parents had left. You will keep all your items and food. And the Awards too.