that you wish you would have brought with you?
Popcorn salt.
That is the only item I have not been able to find (or easily substitute) here in Hong Kong.
Now, if your question is as I suspect, what should you be sure to bring to Hong Kong, that's a whole paragraph or six on suggested items you should bring. Are you looking for some packing guidance?
Are you female or male?
Really, you can get most food stuff here. I would say BBQ sauce, but even CitySuper has Stubb's BBQ sauce direct from Austin.
I am a mid 40’s male. I was thinking along the lines of; corkscrew, can opener, humidor, Scotch, dishwashing detergent, toothpaste, deodorant, etc. I know this all can be purchased in HK.., but perhaps not my particular brand of toothpaste etc.
How expensive is whiskey?
Those daily essentials, toothpaste etc, just try local brands, no need to get hooked on those kind of things, it's part of the fun of travelling.
Hong Kong certainly has corkscrews available for purchase, nice ones too.
Whiskey isn't particularly cheap, buy duty free whenever you can.
Deodorant/antiperspirant have to search around a bit to get some of the American brands- there are some stores that specialize in selling American products but if you have a particular special brand, bring a few. That said, a lot more things from Amazon ship directly to HK (other sites as well) so getting stuff shipped from the US is pretty easy.
You said you were a man so probably not applicable but hair dye/color in shades other than black/dark brown is difficult to come by...so if you are bringing along a light-haired partner, worth it to pack a few.
As for whiskey, I think you can only bring in a liter or so...not sure of local prices.
Hong Kong has dishwashing soap, can openers (how else would they eat all that spam and condensed milk?!), toothpaste, deodorant. All kinds of things! I know Hong Kong is a kind of island city, but we're not an atoll in the middle of the Pacific. I would even say a lot of people here are snobby about wanting better quality things, so we're furnished with all kinds of imports, even of toothpaste!
If you're very attached to certain brands of things, and aren't somewhat flexible, then perhaps it's not a good idea to come here?
Keep in mind, Hong Kong does not have American-size landfills nor a genuine recycling system for American-style product packaging.
I think the only thing that I have found really difficult are the clothes and shoes for larger/taller people.
"not my particular brand of toothpaste etc."
Well, we can't help you without you revealing what these preferences are.
Google iHerb. You can get a lot of stuff shipped to Hong Kong.
Hong Kong is a world city. You'll survive.