For the extra crops we get a discount. As an example, last year we purchased a bushel of tomatoes when our grower announced that extra quantities would be available for purchase via e-mail. We reserved our quantity a few days prior to pick up and took our tomatoes home at the next visit to the market. We still had quite a bit on our total, so we paid for the bushel using our credit rather than shelling out any additional cash.
On a weekly basis, our grower has two sections at the market, one for CSA members which might have some produce special for CSA members or at the beginning/end of their growing season and one for the public. CSA members are allowed to purchase from either section. I suppose this would qualify as "front of the line" privileges. As far as other benefits for CSA members, we have a few. First, although our membership is one price, our CSA gives members a $100 credit. Specifically, we pay $500 for a season membership and start a season with $600 in credit for purchase. A CSA season usually goes from (approximately) late April to Early September. Additionally, now that our CSA season is now over but the growing season isn't, we receive a 20% discount on all purchases for the rest of the season (end of November). Finally, our CSA has an annual picnic in the summer at the farm, where members bring dishes made with produce purchased from the farm and our growers provide meat purchased from one of the local farms and cooked by an up and coming Richmond chef. I feel like we are getting plenty of value for our membership, we see where our produce is coming from and we maintain an engaged "community".