Think of it this way - you will not see your main luggage until you get to the other end.
Toiletries are the important and a change of undies. You will, after a sleep and to freshen up so pack a flannel in there too.
You will get bored of everything after the first 6 hours. You will have read all your mags, probably got bored of your iPod.. etc. However - fear not.. an odd thing usually happens - you start talking to the other passengers and reading their stuff. Especially if they're on the same set of flights.
Switch your phone off. Then only use it when you're at the other side (turn off data roaming too or face a mammoth bill). Use an iPod or something else on the flight. Oh and cattle class means you'll not usually have an power adaptors. Take a pack of cards or a game that doesn't require batteries.
In case you're caught on a long (24hr) stop over the only thing a hotel doesn't have is deodorant.. as your luggage will be kept in unless you want to re-check it in (not advisable).
If the flight is a set of flights, you'll be on the plane between the landing and take off.. don't expect to get off. I'd usually buy a load of munchies.
Now if you're first class and a transfer then you may get an offer of a hot shower between flights - take it but don't expect to have access to your main luggage.
Check on your flight provider's website for the current 'prohibited' list..