Color coded, drug combination guide. Courtesy of tripsit. This should help everyone that keeps asking which drugs work together.
https://burnersxxx.files.wordpress.com/2015/10/tripsit-drug-combination-guide-tj8at.png
Edit: Here's the references: https://wiki.tripsit.me/wiki/Drug_combinations
Glad to see this submission getting some attention. Feel free to discuss your opinions on the validity in the comments so newbies (like me) can get an even more informed opinion :-)
Nitrous Oxide and amphetamines are not recommended to be combined.
The high from the speed will make you less aware of the high from the N2O, which can cause you to breathe in way too much N2O.
http://drugsinfoteam.nl/drugsinfo/lachgas/lachgas-tips/