I carry a small pack that rides high on my back so that it allows me to sit comfortably on the chair lift.

One of the biggest problems that I have encountered is being on the chair lift when it breaks down. It can take hours to evacuate a lift and you are very exposed and unable to move to generate heat or start a fire.

In addition to what you have listed in the pack I carry:
- Thermos of hot chocolate
- High calorie food like chocolate
- Down Vest or Down Jacket
- Wind breaker if not already wearing a shell
- Balaclava
- Warm mitts
- Space blanket/Bag (I prefer a bag with the foot end cut out so that you can pull it over your head and down around your legs while wearing ski's on a lift and not have it flapping in the wind)
- Goggles
- Sun Screen
- Cell phone and sometimes a radio if skiing in a group

I usually put toe warmers in my boots at the start of the day as it is difficult to place them in a boot if you are on a chair lift

edit:
I used to carry a small foam pad to sit on but most modern chair lifts are well padded which provides good insulation.