You will find five vitamins/minerals/supplements mentioned most often on the Internet for these supposed powers: Zinc, lecithin, L-Argenine, Yohimbe Bark, and Astaxanthin.
Few medical scholars devote their careers to issues such as helping a John achieve two orgasms during the hour of time that he has purchased, so some practical experimentation is required. None of these supplements are extraordinarily expensive. The notorious side effect of too much zinc is gas, so it has to be used in proper quantities. Hard to achieve the second orgasm if she has run out of the hotel room. Some people find that L-Argenine exacerbates mouth sores. More importantly, L-Argenine is known to reduce blood pressure, so a combination of this supplement when taken too near the time a person takes Viagra and/or prescription blood pressure pills could also cause problems. But all of these supplements have been around for a long time. Astaxanthin is a little bit newer - some believe if has a steroid effect of shortening the refractory period.
Walgreens sells products online that combine most of these supplements at a pretty reasonable price. They have Twinlab Male Fuel and Nature Made Astaxanthin. I do not believe either contains lecithin, but a can of lecithin granules is available at any nutrition/ supplement place at a low cost.
Many prefer to get these supplements into their diet through natural foods. Oysters and almonds are loaded with zinc and some guys swear by eating a plate of oysters on the half shell prior to sex. Maybe it was a placebo effect, but I had a session in the morning with a provider once and came twice, worked all day and ordered the oysters at a business dinner preceding a night session. Much to my surprise, I did come twice that night, but she did a fantastic nonstop BBBJTC for fifteen minutes with a ton of saliva for the second one, so I really think it was her and not the oysters. Eggs (the yellow part) has lecithin and salmon has Astaxanthin. I have read recommendations regarding certain berries, but I am skeptical and I have never had the patience to search out exotic berries at stores.
Of course, the prescription drug Viagra is the best of all. Most of these supplements (with the caveat noted above regarding L-Argenine) are in addition to Viagra. These are of course first world issues in countries with expensive sex workers. In some locales, it is less expensive to just buy more time with the lady instead of paying for Viagra and supplements!
I like L-Argenine and Yohimbe. Note that V and Argenine tend to lead to reduced water in the system (you know...more trips).... Headaches (if any) later are dehydration. Drink more water! (No headaches, but more trips). V does not increase libido (IMO). Nor Argenine. But Yohimbe does. (I can't do Yohimbe too much...gets me rev'd up in some way too much... Every other day for me.)
Also...minimal alcohol!
Important are: more exercise (not an Ironman, eh), stretching, sleep (sleep!! you need time to dream!), reduced stress, eat well. eg, not too much food before the 'exercise'.
Feels like zinc and potassium are also helpful. (They say; seems right, but not sure I know that 'scientifically' in my body. I suspect that effects are delay and cumulative.)
Did I mention hydration? The right amount a little before. Not too much, not too little.
Laughter is the best medicine, but you knew that.
Enjoy!
Maybe the best suggestion: Get into her. Tell her you are. Nothing gets her turned on more than knowing you are into her (she needs to believe you are not BS-ing).
Don't try hard. Just mean it. And tell her in some half-way original way. (She might have heard one or two people already tell her 'Wow you are pretty and so sexy.' Get a bit more fucking creative than to just say that.) But, she will forgive all kinds of ineptness if you really mean it (and she feels complimented).
(Example of the opposite: Careful! Let's say she feels in general that her hips are too narrow. Then if you say you love her narrow hips, and she is in a certain mood, it might not help.)
If you do that for her, she will do that for you (well, more chance she will).
Having a turned on women in your arms...good chemical reaction is what I call that!
And especially nice knowing you did that to her.
What goes around comes around.
Also (at the same time): be selfish. Women love that (too).
You noticed that these last two are, logically, contradictory. Be into her AND be selfish. But, figure it out! The answer is 'yes'.
Hope that helps someone. YMMV.