Ensure your child has a quiet place to go to at all times, WHEREVER you are.
Try putting decorations up one at a time each day to avoid sensory overload.
Consider smells, e.g. some children may not like the smell of Christmas trees or candles.
If your child is sensitive to loud noises remove the banger from the crackers.
Pantomimes can be loud. So ensure you get seats near an exit, take ear defenders, and a comforter. Make sure there are two adults so your other kids don’t need to leave if your child struggles.
If your child likes to play with the decorations consider buying a second cheaper tree that your child can play with and explore.
An afternoon walk can help. Sometimes just getting out of the house for some fresh air can make all the difference and clear your head.
Wrap presents in easy to open coverings with little tape to avoid tactile sensitivity issues.
If your child loves lights let them put them on the ceiling instead of the tree to avoid any tree accidents if they are too tempting to resist.
Bring your child's tent / own chair into the lounge for family movies so they can be in the room but escape if needs be whilst still feeling included.
Some children struggle to wear appropriate clothes when its cold. Visual support and social stories can help with this- http://do2learn.com/picturecards/printcards/selfhelp_clothes.htm (dotolearn.com)