I laboured in the bath with DD1 and then got on the bed for delivery. I enjoyed lying back and sort of 'floating' (as much as you can in a bath) between contractions but also found that all 4's was good for me too. DH spent most of the time sitting on the edge of the bath and rubbing my lower back through contractions etc. I stayed in there pretty much until I had to get out - my hospital didn't allow water births and at 9.5cm dilated I was unconsciously pushing so started to tear.
With DS I jumped straight into the bath when I got to the hospital, well after the first lot of monitoring lol. I didn't find the bath as good that time though, probably because I was having to get out a lot to go and sit on the toilet. At about 6.5 cm dilated my midwife had an awesome idea and went and got one of the new birthing chairs that had literally been delivered to the hospital that day and set it up in the shower. She said so long as the water was just going down my back and not over my front she'd let me deliver there so that I could have water as part of my pain relief the whole time but it still fit with their 'no water births' policy because there wouldn't be any water over bub's face as they were delivered. DH got the 'wonderful' job of sitting there holding the shower nozzle in the right position so that no water was going over my front smile
With DD2 I planned to do the same thing that I'd done for DS but was at a different hospital and that hospital wasn't able to get gas into the bathroom so I didn't use the shower but did use a birthing chair like I had with DS.
I didn't have anything particularly for the bath, I had a top that I thought I'd wear in there with DD1 but once at the hospital I didn't even think to grab it out, just stripped off and got in the bath. I did take music to listen to and played it using a cd player provided by the hospital for DD1 and on an ipod thing of DH's with DS and DD2. A change of clothes for your partner is probably a good idea though, they're quite likely to get wet if you spend some time in there, even just when helping you in and out smile. Maybe some aromatherapy candles if that's something you enjoy, and possibly consider having the lighting dimmed down if possible but that's more personal preference and what the hospital can do rather than things to actually take with you. For me I tried to make the room as relaxing and stress free for me as possible so had music I liked playing and lights dim. It didn't seem to slow down the speed of my labours (DD1 was a 6hr labour/4hrs at the hospital, DS was 3.5hrs of labour/2hrs at hospital and DD2 was just over 2hrs of labour as counted by the hospital although I'd been aware of lighter contractions for 12hrs before that/1hr at the hospital) but it certainly helped me to get into a good head space for the labour.