If you haven't any heat, you can still start anything that is hardy. I aim to sow broad beans, spinach, peas and sweet peas as soon as I get organised, and certainly by mid Feb, as well as other salad leaves, winter-hardy types of lettuce, rocket etc. I'm also going to do some annual flowers that take a long time to get going: cleomes, leonotis, scabious.
This is especially important for me as I have (relatively) limited space so I like to get in 2 crops wherever I can, so a good early start by being able to put the above out in March (with cloches/fleece if necessary) is very useful. If I had a full-size allotment I possibly wouldn't bother, although it is still lovely to have peas/sweet peas/broad beans by June - and in favourable years, by the end of May - and fresh salad leaves in April.
Of course, if it is solid snow in March/April, I will be stuffed! It's a gamble, but I think it's worth it, it cheers me up no end to have green shoots coming through.