For me it's all about the charity and doing what is right. I generally use my own stash yarn to knit with. Patterns are nice if you want something particular. I have used patterns, but not always. Depends on what it is. I rarely get involved in events, but I have.
I've always liked charities that have a website. It feels official and the info required for the items is in one place. Info such as preferred yarn fiber, sizes, patterns, item needs, etc. if you don't have a website it might be a good idea.
Shipping to the UK would be too expensive for me personally, but we have some members here from the UK.