Looks like you have a number of good replies. For the lighter stuff,
maybe chips or whatever, a good tarp with a pile of the stuff on it and
a couple small ropes would move it uphill with 2 people fairly easy.

Greg wrote:

Hi. We'll be cutting down trees, removing overgrown brush, etc. from
about 4000 sq. ft. of our downsloping lot. I've rented a large green
waste container, but can anyone suggest an efficient, cost-effective
way to get the stuff we cut uphill to the container at street level.
It's not possible to get any type of vehicle behind our house.

Right now, we're just thinking of putting as much as we can in either
boxes or heavy duty plastic bags, and having two people carry one of
these up, then repeat (and repeat...) I'll have two other guys
helping me. Thanks for any help.