My frugal and energy efficient grocery getter..
Here's what I've been using lately do do my shopping, it's working pretty well for me so far. If I dress reasonably warmly I can ride down into the thirties without getting too uncomfortable, a little vigorous pedaling is remarkably warming. I've managed to carry two weeks worth of groceries plus a medium bag of dry dog food and not felt the trailer was overburdened, I could have carried another bag of dog food easily. The arched sides of the trailer fold upwards to make a frame for a nylon enclosure that is very nearly weather tight and easily as big as some car trunks.
I've had the bike for going on five years now but I just got the trailer this summer, both found on Craigslist. The bike is lighter than it looks and far superior to a regular bicycle for anyone who has back or neck problems, it's lovely to actually be able to look around at the scenery and traffic and not focus ten feet in front of your front tire. I go two miles on a regular bike and I'm in pain, I've done thirty plus on this without a problem.