Not all of it is necessary. A lot of it you need anyway like the stuff for the baby and just general clothes for you. If you don't have enough PJs and don't want to buy more - loose fitting shorts and t-shirts will be fine. The hospital staff aren't going to criticise you for what you wear to bed, but it is nice to have clean clothes if your PJs get soiled. You can always send thing home with your DP to wash and bring back (it is a lot of pressure for him though) if you don't want to buy more.

When I went to hospital to have my first baby, I sent a list home with my DH for all the extra things I needed that I didn't realise like extra clothes and Pjs. Then I didn't end up staying after the first night anyway so I didn't need it all, but you could wait and see and ask DP to bring extra things from home.

Most of it depends how long you plan on staying . . .