Posted: 02/05/2015 at 23:44
Ivy and ox-eye daisies perhaps but you must have the landowners permission to explore & pick. Only take a relatively small percentage of what's there - making sure you leave roots and seed heads so the plants can reappear next year.
Personally, I would not rely too heavily on foraging unless you have a reliable source on your doorstep. It could all be quite time consuming at the very last minute. Foliage will almost certainly keep well for a few days in a bucket of water in the shade - but wild flowers are usually quite ephemeral & need to be gathered the night before (even on the day) and, if it's raining, they will look rather bedraggled.
Better, I think, to plan to only use something like the cow parsley to make a last minute informal display if it's looking good on the day.
Now is the time to find out where you might be allowed to pick some - try to find several sites with different conditions - plants will mature at different times depending on whether they are shaded or sunny
In friends' gardens you might well find some lovely weddingy flowers such as anthemis, ammi major and feverfew - these always make lovely frothy mini-arrangements for placing along window ledges etc. If you have enough they will supplement larger arrangements too. I often use things such as dill or fennel in flower arrangements - the foliage is light and ferny and the flower heads are beautiful.
You don't necessarily need a lot of flowers - single stems of anthemis, zinnias, carnations, cornflowers etc in tiny containers (even test tubes held upright in sand or a block of oasis) can look stunning placed in a line down the centre of a long table.
Sarah Raven's website usually has some good ideas for very simple & more complex flower arrangements. Hope it all works out and everyone has a great day