Good instant coffee available everywhere in Vietnam
One of the downsides of trying to eat almost anything in Vietnam, and from what I hear all the surrounding countries is that no matter what it is that you are trying to buy it is almost always going to be completely loaded up with sugar or some sort of sugar product. We haven't quite gotten to the corn-syrup stages here like they do in USA (thankfully) but if you buy something in a store thinking that it is something like what you have back home and then you get home and it tastes like it is 2/3 sugar just know that you are not alone. Especially in minimarts which a lot of people use for most of their food over here, the products that are readily available almost always have added sugar.
Does this make it taste better? Of course! But I for one am not really trying to sprint towards diabetes so I would rather not have everything that I do contain a bunch of processed sugar.
Coffee in Vietnam is available everywhere and almost all of these places are going to absolutely load it up with "condensed milk" which is a product that I am amazed they are still allowed to call it that.

I drink a lot of coffee but I am not at all interested in drinking a couple of candy bars because I am in this game for the caffeine, not to have a 400 calorie drink. I have made a lot of mistakes in my time here purchasing this thing and that hoping it was a sugar-free one but I have finally found a widely available instant coffee brand that is available almost anywhere.
Trung Nguyen is the brand name and you can easily recognize it by the red and black container it is in. Idon't expect you to remember the name because I never do They normally position it very near the Nescafe because of the similar color scheme. I believe this is a bit devious on this product placement but Nestle is kicking everyone's ass in the coffee industry so I don't think they complain.

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You do need to be a bit careful when you are shopping because the boxes all look the same and while this one in the picture is in English, most of them are not when you are here. The first one is pure coffee, the second one has sugar and milk product in it and is so sweet that I find it undrinkable.
If the packet is a long tube, you know you have the wrong one because the coffee portion of that dry mix is actually a very small packet on its own. For people that are accustommed to what sugar-packets or packets of Sweet n Low used to look like, that is what the sugar free one looks like now.

The packet is roughly the size of a business card and it is only 2g in total weight.
It will make one cup of reasonably good-tasting and totally sugar-free coffee for your house or hotel room. For me, if I need a real pick me up I will drink 2 or 3 of them in one cup like a lunatic.
Going out for coffee is easy and cheap here but you always run the risk of someone presuming you want the super sugar version because that is the default in Vietnam.
I bet this will maybe change as their population is starting to see a rather large amount of weight gain and even problems with obesity for the first time in Vietnam's history.