I have not ever used anything in my ass during masturbation sessions. Now, my wife controls all my time spent in self-pleasure and she loves to have me masturbate while one of her bulls watches me. She will often give me one of her toys to have inserted in my ass during this time. Either she or her bull will often insert it.
Most common items I have in my butt:
1. Dildo - normally as deep as it will go.
2. Butt Plug - again, all the way in so that only the handle is outside me.
3. Long Neck Beer Bottle - Yep, her one boyfriend has a fetish to press the neck of his Budweiser inside me.
4. Fingers - her bulls or hers but at times I am told to push my own finger inside myself, I go knuckle deep but up to her.
5. Various Toys - my wife has a wild imagination, so I have taken a lot of toys up my butt from time to time.