Declining an invitation

• That sounds lovely, but I'm going to sit this one out. Have a wonderful time.
• I can't make it this time, I'm afraid. Thank you for asking me - it genuinely means a lot.
• We're keeping that weekend clear, so we'll miss it. Let's do something just the four of us soon.

Declining a gift

• That's so kind, but please don't - your being there is the present.
• We really don't need anything this year. If you'd like to do something, a card we can keep is perfect.
• Thank you, but I'd feel awkward accepting something that generous. Can we call it even with a coffee?

Declining a favour or a collection

• I can't take that on at the moment, sorry. I hope you find someone who can.
• I'll pass on the collection this month, but do put my name on the card.
• I'm not able to host this year. Happy to bring pudding wherever it lands.

Offering a smaller thing you can do keeps the no from sounding like a door closing.

If they push

• I know, I'm sorry - it's still a no from me.
• I've had a proper think, and my answer hasn't changed.
• Let's leave it there. I'd rather not go round again on it.