Robo gels are the way to go, but I always just put an unquestionably lethal dose in a half-full water bottle and take a big swig. The promethazine I'd avoid just because it doesn't really seem necessary or a safe combo, but the Benedryl I'd do. It's not physically dangerous, but frequent dissociative users like me experience heavy HPPD, and even a week-long binge on either DXM or Benedryl alone will most likely result in a permanent damage, but it'll just mean you'll see certain DXM/Benedryl related shit possibly for the rest of your life. If you're cool with having serious trouble with facial recognition or non-stop twinkling of everything, go fucking crazy. If not, do it once, three times if you like it and never do it again.