When we have 100 days left I find a jar that 100 quarters will fit in (small jelly jar). My daughter gets a quarter each day for something she does to help plan/prepare for the trip. (okay we stretch this sometimes....on a really busy day we say that just happy thoughts count) When the jar is full, she has $25.00 extra to spend (she saves up all year long and usually has over $200 to take for herself).
and just a side note of how we keep track of all her spending money. She has a checkbook register and makes deposits in "her account" (bank MOM) When we get to Disney, she withdraws $20 a day and buys Disney dollars to spend that day. She can either spend the whole $20 or save it and have $40 the next day. My daughter loves to spend it all at once and so we do not have to tour every giftshop all day. This has worked for our past 4 trips and we love it.