I'm based in the USA and our elementary school (700 pupils between 5 and 10 yo) uses hundreds of volunteers a week doing the following:
Library duty (shelf stacking, shelf reordering, checking books out and in, covering books, preparing seasonal wall displays)
Lost property
Room Moms - organising class social activities, gifts for teachers etc) they organise the class contributions to teacher appreciation week and the staff Christmas lunch. They write a monthly newsletter too.
Math challenge volunteers - 2 or 3 parents one hour a week to help uppity children's math challenge games
Reading volunteers- one volunteer per week per class to read a story/poetry to whole class
Class prep - variety of work including stapling, preparing wall displays, separating worksheets, laminating. One or two hours required per week.
Photocopying - a list of copy requests are left by teachers in the copy room and volunteers come in each day to complete on a rota.
In addition we also have committees of volunteers who plan, run, decorate for and recruit others for the following:
Annual Fall and Spring book fairs
Annual sponsored run
Annual Science fair
Annual Science day "camp"
Annual school movie night
Annual Spring fundraiser (similar to a fete)
Yearbook (huge amount of work)
School store - sells school t-shirts, water bottles etc
Run the PTA website.
Organise photo days
Organise school supplies sales. (You have to provide all note books, pens, scissors and glue etc here)
Field Day (sports day)
School Concerts
Junior Business programme
Why not survey your colleagues- see what help they need and then see if there is a way for volunteers to fulfil it?
The volunteers at our school include scientists, lawyers, engineers, teachers, professional artists and musicians, accountants and IT consultants. Many of whom are now SAHMs or SAHDs and have time and energy to contribute.
These are serious people - our PTA raises more than $200k each year.