I have attempted to ctb once and I was smoking weed and DMT the whole time.
I strongly advise against shrooms or even LSD because they can make you throw up (unless that doesn't matter to your method, obviously).
On the other side, weed is good as an anti-emetic. And DMT... DMT was an amazing choice.
DMT is released naturally by the brain during a near-death experience and during actual death, so smoking it before dying just kinda made sense to me. It made me feel safe and prevented SI from kicking in. 100% will do again.