Do you love your picnic mat?

[TW2013]

I am looking for recommendations for a picnic mat as it looks as if picnics will feature heavily in our summer plans- it needs to be:

1. Waterproof- UK, say no more!
2. Large, 5 people and the children just keep growing!
3. Fairly plain- not keen on stripes or spots.
4. Available on line.

Any recommendations?