Agree with loads of the above. Arnica was brilliant. I was really, really bruised from the scar down to the tops of my thighs (midwives said they had never seen anything like it) and it was almost gone two days after taking arnica tablets.
Surgical spirit is useful to remove the incredibly sticky residue left behind by the dressing.
I had my C-section at 9:45pm and was out of bed going to the loo on my own at 8am the next morning (midwife accidentally took out my catheter early) but it was fine. Try to stand and walk straight from the start - it's easy to hunch over so as not to put pressure on the scar.
Definitely second getting the call button and anything you'll need to access (drinks, mobile phone etc) put as close to you as possible - I couldn't reach the call button and ended up holding my son all night after a feed as I couldn't call anyone to put him back in his crib!
Earplugs and an eye mask a good idea - if you're on a ward with others as I was, all the babies cry at different times and lights are on and off all night which means you get bugger all sleep, and sleep is what you need!
I had some big incontinence mat things which I put under the sheet at home in case my waters broke in the night, which came in very handy to change baby on while in hospital - you have to do this on the bed and it's not very good if they wee all over everything! I found hospital beds exactly the wrong height for nappy changing after a C-section - my back ached like hell.
The worst bit of the whole thing was having to get the dressing off the wound after the first day - was told to go in the shower and thoroughly soak it and take as long as I liked. The dressings they use are so sticky I was in the shower for 45 minutes and came out looking like a prune. Had to ease it off bit by bit as obviously did not want to tear anything!