Raising money by a non-uniform day
Have a fun day and invite people to go to school or work (especially for those who work in an office) dressed according to some given theme.
Charge those who don't join in, only £1 or £2 (it is not a punishment!).
Collect donations from everyone , especially the boss or the head teacher etc.
Make sure that you have lots of information about the charity you are supporting. You could even invite people from the charity to attend during the day.
The main point is to have a fun day