Please no dreadful poem. I hate them.
I think it's nice of your friend to specify what the cash is being used for. I much prefer to give cash if I know where it is going.
"We are lucky enough to have our own home set up so we don't need many gifts. We are planning a honeymoon a little later in the year and we would truly appreciate any contribution you could make towards that. There will be a wishing well at the reception in which we would love to receive your greeting card and a cash gift. Alternatively, XXXXX has a list with a few gift ideas and may be contacted on xxxxxx".
Bookmarks