I have found this short article:

How to survive gatherings

Being amid large groups of people can be enormously stressful for people on the autistic spectrum.

Some steps you can take as a family to make the experience not only easier, but actually enjoyable for autists:

  1. Be sure that all family members discuss what is most likely to take place on that special occasion.
  2. Remember that most people on the spectrum do NOT like surprises.
  3. Negotiate how long the AS person has to stay in the special environment. If the occasion is taking place at home, work out how long the person has to be with the group before they can go to their room or leave the gathering.
  4. Discuss whether or not the AS person or any other family member will be expected to behave in a manner that is out of the ordinary. Some “role playing” can be a fun activity in this case.
  5. Discuss what the AS person will wear.
  6. Talk about how most people are likely to behave in the situation. Will there be lots of laughter…music…games? Will lots of kids be there? Will the AS person be expected to perform any duties or sing or play an instrument or a game?
  7. Share why you want to or must attend this occasion.
  8. If an amount of travel time over what is usual is required…or a different form of travel is involved, estimate the time and/or mode of travel and talk about things to do during that time, what to bring along to be comfortable and points of interest.
  9. If the gathering or occasion is highly distressing to the AS person, carefully discuss whether or not to continue  participating in the occasion.