What about having a big garden bag at home - does anyone do that? Surely you could work out a better rate with the supplier and have 2+ bags, they know they're going to get business from you and with multiple bags it's good for them because they don't have to drive all over the place... I've been thinking about that myself recently.
I used to be able to get away using customers green bins (or even my own rubbish and green bins) but sometimes there's no way around it, PITA when you need to go to the tip just for 40kg worth of bulky nuisance trimmings (not just grass but plants, shrubs, trees etc.)