I have been using K20 Protein Water mix made by Kellogg's. These are individual packet servings that you can add to 16-20 oz. of water and it gives you 5 gms of protein. It also comes in premixed bottled water but I have only tried the individual packets which have pink lemonade or iced tea flavors. I love the pink lemonade and I just bot the iced tea. It really helps me feel satisfied while on the go
EDIT: sorry my solution is not a flavorless one :huh2:. They do make a whey Protein powder that is "flavorless, natural flavor". I use the GNC brand as they readily stock it. It contains bout 20 gms protein. Hope this helps. There are a lot of different brands and types.