This is a good starter pack and includes 3 different sizes to wrap different foods and to cover a range of needs.
The 40cm is big enough to cover must mixing / salad bowls and will wrap a small loaf or wrap a large sandwich for a greedy picnicker! They are good to use to cover rising dough and easier to clean than a tea-towel!
The 30cm is a good size for a round of sandwiches or a large chunk of cheddar. Or to make a folded snack bag.
The 20cm will cover smaller bowls, wrap smaller pieces of cheese, keep half a lemon fresh and cover that half tin of baked beans in the fridge.