Next time you are invited to a meeting that you think is a waste of time; calculate how much money it is costing you personally, and how much it is costing the business. you can do this yourself or you can get everyone in the meeting to do it.
Calculate your average hourly wage (salary/52 weeks/40 hours). If you do this as a group ask each person to do the maths then give it to you on a scrap of paper so you can add it all up.
Now stop wasting time doing silly sums and get on with your meeting!