I have permaculture farm in Finland, Ikaalinen (61.816494N, 23.214763E). Climate type according Köppen classification is snow- and forestclimate moist- and coldwinter type where warmest month average temperature is minimum of +10 deg C and coldest maximum of -3 deg C and where in all season precipitation is averagely moderate. Typically we get the last frost in June and after typical sunny summer first frost in September.
I've got a lot of heirloom varieties growing on the perennial side, including very hardy berries (blackcurrant, redcurrant, strawberry, gooseberry, sorbus, blackberry, raspberry, common sea-buckthorn) apples and damsons.
One very prolific plant I grow for edible seeds is http://en.wikipedia.org/wiki/Angelica_archangelica
maybe these could do fine also in Iceland, in case you would like to get some finnish heirloom variety seeds (at cost + P&P) please let me know. There is reputable source for these called Maatiainen which is kind of "living seedbank" for finnish heirloom varieties. http://www.maatiainen.fi/english.htm
The latest catalogue of ornamental (note; many of them poisonous) and edible heirloom varieties available
I'm also experimenting quite a lot with wooden-stem plants (full list of species found in Finland http://www.metla.fi/metinfo/puulajit/puulajinimiluettelo.htm
), growing from seed and checking whether successfull on long term. Have had some great succeess with linden, elm and oak in areas which have nice microclimate, but not yet with hazelnut and sorts of more delicate coastal area species (typical trees for the area are pine, spruce, alder, birch and willows).