Whatever you would take in an overnight bag, like if you were staying with a friend or at a hotel. Clothes to come home in. Extra socks - hospital floors are cold. Pads (don't forget those!). A book. There are lists of stuff you should take - but I don't think the majority of that stuff gets used. Think about being away from your house for a day or two - what would you want with you?

Ok this is a long list that my midwife gave me so bear with me: (these are only the essentials!)
for mum: drinking water, water sprays, flannel or natural sponge, ice cubes in a flask, healthy snacks, cds (music), things to remind you of home, magazines or easy reading, comfy clothes. Pillows and cushions, bean bag and inflatable ball, disposable knickers/old knickers, change of clothes, maternity pads, lip balm, toileteries, towel, overnight clothes, dressing gown, chocolate rewards!!!! Lol
for dad: drinks, snacks/sandwiches, change of clothes, camera, change for car park/vending machines/payphones, list of people to phone
for baby: nappies, baby clothes, a blanket, cotton wool
hope this helps x