I try to eat most of my food in season so occasionally, people ask me, what do you eat in the winter? What to eat in the summer is a no-brainer, but in the winter it is trickier. I rely more on frozen or canned items that were picked and put up in their prime- often they have more nutritional value than "fresh" items that were grown two continents away, pick prematurely, shipped here and ripened and kept from early decay by means of ethylene gas and such. Yes, frozen, dried, and bottled can be a good resource in the off-season- even if you can't do it yourself- go with a brand you like that isn't adding in extra stuff or preservatives.
Though, I also do manage to eat fresh foods that are in season (even here in Maryland) in the winter. Lots of local farms offer greenhouse greens and other hearty greens like kale continue throughout the year. And cold storage items also keep us going around here. For more information and so links to great recipes check out this link: 10 fresh in season vegetables the east coast should be eating now.