PPH guidance states that the Tagamet (800mg) (or, alternatively, PPIs Prilosec 80mg or Nexium 80mg) serve to potentiate the SN by reducing stomach acid and increasing SN absorption. Yes, they do have different MoAs but apparently can generally serve the same purpose with SN, although they do suggest Tagamet over the others.
PPH recommends taking metoclopramide (30mg) about 40 mins prior to SN, and says that the Tagamet (or PPIs) can be taken at the same time. Of course, the meto is to help with nausea/vomiting/stomach emptying. They also suggest taking the meto with ondansetron (8mg), although I'm not clear on the reasoning behind this. I didn't get any myself.
In short, the PPH says all of the aforementioned can be taken together with minimal tap water about 40 mins prior to taking SN (25-35g, depending on weight).
Finally, PPH recommends taking 800mg of propranolol along with the SN (can be crushed and mixed into same glass) in order to potentiate the SN and also minimize the discomfort by making you pass out faster.
Hope this is helpful (and that I'm not breaking any copyright laws