I am slightly reluctant to recommend foraged weeds on a non-specialist forum with an international readership, as there are numerous poisonous weeds growing alongside common and delicious varieties, and the flora of the British Isles is different to that of New Zealand, say.
In the Apiaceae family, most prominently...https://en.wikipedia.org/wiki/Apiaceae
... there are wild carrots, wild parsley, angelica, fennel, etc. Also, and very difficult to distinguish, unless you are a Botany PhD, there is hemlock, fool's parsley, Satan's parsley, all of which are very poisonous. So be careful.
Secondly, if you have any known strong allergies, be very wary of any foodstuff which is unfamiliar to you.
Third, beware also nutters with sprayguns full of Roundup and other poisons blasting away at everything they can see.
With these caveats, the gathering and consumption of wild plants is a fantastic way to reduce your environmental impact; a huge amount of European salad is now grown in semi-desertified parts of Spain, by irrigation, then exported by road transport via Amsterdam to all over Northern Europe. The export of 97% water from Spain to Wales, say...
Meanwhile, in Wales, the happy shopper is paying up to £20/kg for some "healthy" salad, if they are buying bags of mixed leaves, which are mixed mainly with air, and wrapped in a plastic bag to deliberately maximise the volume of the package transported. At these prices, an average Welsh ditch contains around £5 of salad leaves per metre squared.
In the past, many other plants were used as foods in the British Isles. A Shakespearean-era salad, or sallet, would typically consist of up to 40 commonly-eaten plants.
Here are some...https://en.wikipedia.org/wiki/Alliaria_petiolata
Garlic mustard has a much stronger taste than "wild" rocket; it is actually closer in taste to the cabbage family. There is no finer possible addition to a sausage sarnie.https://en.wikipedia.org/wiki/Aegopodium_podagraria
Ground elder - IT MUST HAVE A TRIANGULAR STEM CROSS-SECTION - tastes of celery, but much nicer.https://en.wikipedia.org/wiki/Taraxacum
Dandelion makes a very good addition to eggs mayonaisse, say. As the French common name, pis-en-lit, suggests, it is a strong diuretic.
The following link has some extra information for UK readers...http://www.wildfoodschool.co.uk/urban/wfsURBANGUIDE.pdf
...and an ever-increasing number of other guides, courses, etc, are becoming available.
Also recommended, as they are both clearly not actually trying to sell you summat are the works of this pair...https://en.wikipedia.org/wiki/Nicholas_Culpeperhttps://en.wikipedia.org/wiki/John_Evelyn