People want to know about what he meant to you, and funerals are shitty places to be without humour.
Write a short but humorous piece about you and him and make them laugh.
Then sit and read it 5 times, stand and read it 5 times until you can do it without notes.
It's a performance, make it a good one, make it funny, make it heartfelt and only cry at the end.
It's a tough call but my advice from personal experience; get your race face on and give it your best shot.
You're not doing it for you, you're doing it for everyone else, so make it the best that you can.