I took a small suitcase,seemed silly to pay good £ for a bag.As for size its up to you.
In retrospect firsttime out I packed loads of uneccessary crap.
Essentials are:
Maternity pads,more than you think you will need!I only put in one pack...bad mistake,the lochia was like the worst period you could imagine x10,so more than 1 pack!
Don't think you will get into your pre preg clothes straight off,was gutted when I realised I couldn't get into my size 10 jeans,stick with maternity clothes (WHAT AN IDIOT i WAS)
Lots of old/cheap knickers you can throw away.
For baby,pack of nappies,wipes or cotton wool
Vests
Babygros
Cardies
Hats
Bottles of water/juice
Snacks
Toiletries for yourself
Dressing gown
Slippers
Anything else can be brought in later