Fresh Direct vs. the local grocery store

I admit it. For a while now, I've been shopping at Fresh Direct 2-3x per month. In some (suburban and rural) places, grocery shopping  by delivery actually makes good environmental sense, since there's only one truck driving around making several deliveries, instead of all of those cars being on the road. In New York City, though, it's not clear that it makes the same good sense, since otherwise we'd be walking to the store or taking the subway. Sure, it's more convenient, which is why people do it, but it's not necessarily the environmentally conscious choice. In addition to just having the trucks on the road, they're also a nuisance in many neighborhoods, because they double park and idle with their refrigeration units on. Furthermore, FD food is delivered in cardboard boxes, and loose items like olives come in high-end plastic tubs (not the kind you feel OK about throwing out).
So with all of this in mind, I decided to go to the regular grocery store yesterday. I took three canvas bags with me, and bought probably a little less than the normal 10-days worth of groceries that I'd otherwise get at Fresh Direct. And you know what? Even with FD's delivery charge and gas surcharge, it cost me $20 more for the same type and amount of groceries (including about the same mix of organic and conventional foods that I normally buy).

I am willing to pay the price premium for organic foods, and when the Greenmarket has better offerings than it does in the dead of winter (mostly baked goods), I pay a high price for locally produced foods. But do I suck up the extra $20 a few times a month and stop shopping with Fresh Direct? Would it be an adequate compromise to shop there once a month (thereby cutting down on trips and packaging)?

I suppose I should be happy to be fortunate enough to be able to consider the environment in this matter, as many people would simply only be able to do whatever is cheapest.