10. Make him feel better and say, "No no no your gift was much better than Abel's."

9. Tell him he has a great view on holiday shopping.

8. Ask him how his brother is.

7. Ask him if he wants to help you build a city.

6. Ask him to sire children for you to diab, so you can be second gen.

5. Tell him about the trouble you have had lately with your childer, complain about how they never listen and are always fighting.

4. Ask him if you can make out, and give him a really nasty hickey.

3. Ask him if you can dance with him.

2. Offer him a Mentos.

1. Buy a big foam hand with a #1 on it and run after him chanting "Caine's Number 1!!"

P.S.:
Other ideas for fun with Caine

If the rumors are true and God will do sevenfold what you do upon Caine, then give him a dollar. When God gives you $7, give Caine those $7, when God gives you $49, etc. etc...