Strawberries are actually native to Europe. The modern variaties are based on hybrids from South America. The native European species were edible though and were eaten. Many fruits were present in Europe. The Romans spread grapes and likely apples and pears. Brambles and raspberries, currants and many more are naturally found in European woods. Quinces, medlars etc. also grew. Many of these can be stored or dried quite well. Cabbage, onions, peas and broadbeans, beets, many radish like plants, other greens, carrots and relatives of them are also all native and were eaten in some capacity. Many common garden weeds are native to Europe and edible. Dandelions, stinging nettles etc.
Hello, trained historian here, who worked extensively with the medieval era. So, what did old-timey people eat? In Denmark, we're mainly talking about a diet without much meat. Only the richest nobles could afford to eat meat dishes every day, and for the vast majority of the population, meat-focused dishes was a luxury, largely reserved the major holidays, such as Christmas and Easter. Ofc. meat was eaten, but not in the same style and context as today. It was mainly dried, smoked, or preserved in other ways. It wasn't a fresh roast or piece of steak. Contrary to nowadays, beef and mutton was, for a long time, the main eating animal in Denmark, before pork took over, pork being regarded as a luxury in medieval times. Poultry wasn't really viable, not even for the richest, outside of special occasions. The only widely available meat, was fish. Particularly herring, which the Danish belts floweth over with, so much so that the main income for the Danish state for a long time, was taxing the Scanian herring-markets. It was crazy how much herring was pulled from the debts. When the small silver suckers stupidly migrated through Øresund, you could practically pick them out of the water with your bare hands. So, if meat was off the table, bar at holidays, what else did people eat? Ofc. fish, but also porridge from barley, or oats if you were fancy. The first price however, was cabbage. Cabbage was so important in medieval Danish cuisine, that the oldest Danish word for garden is kålgård, meaning "cabbage plot." Peas were also extremely important to Danish cuisine, in multiple forms, but not the modern green ones, most people think of... Mainly the hard yellow and grey ones, that were dried and needed to be boiled or stewed for a long time to be edible. Ofc. there was also things like bread and such. Onion and garlic were known to be used as sources of flavour, since spices weren't a thing most people had access to. Various fruits, apples and plums and such, were also popular, particularly the apple, with many of even the poorest farms having an apple tree.