Several of us found that it took a few days to get accustomed to the taste of Huel by itself. You may experience this as well.
I can offer a lot of options for flavoring, but most really need a blender (which is how I make all mine). Frozen berries, half banana, unsweetened Apple Sauce, peanut butter, cashews, cinnamon, etc. Those are mostly what I use.
I suppose if you need a single additive that can be shaken, then a packet of hot chocolate mix tossed in with your Huel could do the trick. Perhaps sprinkling a bit of cinnamon sugar or cinnamon powder could do the trick.
If you had access to powdered peanut butter, that could be added and shooken. (Is shooken a word? Looks weird when I write it.)
If you like coffee, I wonder if there are instant coffee or capachino powders.
The chocolate or caramel syrups that people add to their coffee could be another additive that would probably dissolve in the Shaker.
Don’t give up. Most of us weren’t blown away by the taste on first try, but stuck it out. It works so well for many of us.
[Get a blender. Blend it before work. Put in thermos or bottle. Take to work with lunch bag and cool packs. Super easy and a lot more options for flavoring.]