At the Etape there can be a fair bit of waiting around so take plenty of clothes, better to be too hot than too cold. Most arm and leg warmers can pack down pretty small, if you only have heavy legwarmers buy some knee or light weight lycra ones. Don't be fooled by the weather forecasts, the Pyrenees can be very wet even in the height of summer so a waterproof is a good idea, one with a hood is perfect for waiting around before the off.
Carrying stuff is a bit of a pain but don't be tempted to travel too light as the weather in the mountains can turn very quickly. In 2000 on Mont Ventoux several people were hospitalised with Hyperthermia, it was literally freezing, started snowing at one point and we were all in summer jerseys. So you MUST carry arm warmers, leg (or knee) warmers and a decent gilet with a windproof front. Wear mitts (your hands will hurt after 180 kms of hills) and, if you can fit it in, a lightweight rain jacket. All this needs to go somewhere when (if) the sun comes out so don't forget the sun cream. With all this kit to remember, you're going to need a jersey with deep pockets.
OK so a saddle pack looks horrible, but I like to use one to hold all the tools and heavy stuff. There's nothing worse that saggy pockets and heavy stuff bouncing around whilst you're climbing. Your mobile phone may want to be closer to hand in your pocket but it can be wrapped in cling film to stop you sweating into it and ruining your pictures, you can still use it too.
2 x inner tubes
1 puncture kit
mini pump (one that you know works!)
Jersey pockets should be reserved (as much as possible) for food and clothing. You shouldn't really carry tools and keys and stuff that's sharp anyway - just in case you fall and stab yourself. Mini pumps usually have a bracket that can attach to the bottle bosses.
Drink plenty of energy drink before you start and take two FULL 750ml bottles on your bike, one quite concentrated and one weak so you can alternate to suit your taste. Again the refreshment stops will have isotonic drinks to fill up. Remember to stop to have a long drink and before you set off again fill up your bottles. If it's hot, hydration will be a major factor in finishing in a decent time and in a decent state.
You should have already practised this (see John's article) in training. I can't stress enough to only eat and drink stuff you are familiar with. I tend to start eating early, after the first 30 kms or so. Remember to drink a mouthful every twenty minutes and keep in mind that you don't want to be hungry or thirsty at any point, it's too late then. Try to pack things that you will look forward to eating too, Rice Krispie squares are my favourite as they are so much easier to eat than Powerbars, easier on the palate too. A chocolate bar will help you through the final 20 kms, but will melt if it's hot so wrap it in silver foil. Actually I take the wrappers off any difficult foods and re-wrap in silver foil as it's easier to unwrap on the bike.
Carrying bananas isn't necessary – as there will be plenty at the refreshment stops. But I carry a couple of small sandwiches for the early hours, then 2 or 3 energy bars, Rice Krispie squares(!) and a couple of gels. Usually gels dehydrate me a fair bit, so remember to drink plenty of water with them - Maxim ones especially. Some riders make a small bottle (the hand-held ones runners use are good) in their pocket with flat coke or strong sweet coffee in it for the final kilometres, when your legs are in bits.
At the finish...
In your kit bag at the finish have a clean change of clothes and a recovery drink (warm banana RE-GO, yummy!). Wet Ones are a good idea too so you can freshen up a bit after the ordeal. There will be a sandwich and a cold drink for you from the organisers so find a quiet place to sit and reflect, remember to eat something straight away. I like to do a short ride after a few minutes rest, just to spin the legs out again. On the other hand, you may just want to find a bar...
Lastly remember although there's a lot of focus on the main event, remember that it's a fun event and to take in some of the atmosphere, it's not a race. Also there are plenty of stands and people to chat to and keep in mind that it's supposed to be a holiday.