I agree that combining your repair kit is a sound idea , but you'd be well advised to all take your own puncture repair kits, pumps, spare cables and set of hex keys. This allows you to make your own adjustment more quickly and repair punctures should one occur whilst you are a distance behind your friends.
Take a pen knife if you can - they are invaluable.
I bring plenty of spare spokes just in case. They are very light so their weight is not really an issue and on a recent tour my friend had 15 spokes break on his brand new bike.
You can cook quite adequately with one of those stoves that screws into the top of a gas cannister and then unscrews when your done leaving it sealed. This is fairly light and doesn't take up too much space, neither does a bowl, mug and cutlery.
I find that one or two large plastic drinks containers are essential. They can easily be strapped to your rack along with roll mat and tent and provide and extra source of water- 1.5 litres in your bidons is not really that much.

Obviously the above is just advice the main thing is tour how you want to.