In regards to your list, Risperidone, Wellbutrin, and Aripiprazole are prescribed for psychiatric reasons. If your planning out a suicide, I'd use these medications as you would any other day, as "messing" with these doses can change your state of mind, which is the last thing you want when planning your early exit.
Divalproex sodium on its own will not contribute to death, but it is a common seizure surpressent medication. If your taking it regularly, I'd continue it's use as directed.
Don't mess with Trihexyphenidyl. It can cause severe neurological issues in high doses. While it is a muscle relaxer, I'd continue it's use as directed.
Propranolol is different from all the other drugs you mentioned. This is a beta blocker, and is even used on its own for suicides. (There are several threads regarding its use, and some members here are even planning on exiting with this method). Most likely, you won't have enough to kill yourself outright, as the dose to bring on acute death is very high. However, propranolol can be incorporated into your plan as a comfort drug as it will reduce anxiety (common off label use) and ease pain from the tachycardia induced by SN.
Take a look at your propranolol. Many people will crush it prior to consumption to force it to work quicker. If your pills are extended release type you will have to crush them, otherwise the effects of them will be delayed and weakened.
None of the medications you listed are antiemetic, so you may want to try and get your hands on metoclopramide. In most of the world, it is available by prescription only. If you can't obtain this, the tablet form of PepcidAC (Famotidine) in a high dose is a viable alternative.
Best of luck on your exit plan, and if your comfortable, please keep updating this thread as your plan progresses.