Blenders are wonderful tools. Almost any food can put through the blender, if it's got a strong motor. Even things like eggshells, watermelon seeds and rinds, and crab shells can be ground up into to digestible size. (Talk about making the inedible and unappetizing edible!) For people who have some problem swallowing and are fed through a gastrostomy tube, you can take pretty much any meal, add a good size glass of milk and liquify it
enough to flow it through the tube. There is not much culinary skill required here, since tube-feeding preparations bypass the taste buds.
However, if you are going to take this liquid food by mouth, you have to think about what's it's going to taste like before you throw it in the blender. I like wine, and I also like it with cheese and crackers, but somehow, the idea of putting it all together in the blender doesn't sound too good to me. Also, some foods will take a LOT of liquid before they start to flow well -- like a peanut butter and jelly sandwich. Pates, SPAM, refried beans, mashed potatoes, a can of minestrone soup, these don't take much liquid to turn into drinkable consistency. You want to avoid natural (or artificial) emulsifiers; lecithin (egg yolks), carrageenan (sea weed), pectin (cooked fruits), to keep the blended product thin and runny.
Another thing to consider when preparing a liquid meal is that digestion starts in the mouth by chewing your food and adding saliva. When you bypass this step, it's advisable to add some extra digestive enzymes in your blend so that food molecules are being broken down even before you swallow. Things to add are: pineapple (bromelain), papaya (papain), kiwi (actinidain), and even ginger and citrus juice, as another post has mentioned. These fruits or juices have to be raw, their digestive enzymes are inactivated by cooking.
Fermented foods are also pre-digested by the fermentation process, and in addition contain live bacteria that can be beneficial to the intestinal flora. Things like sauerkraut and kimchi can be tossed in the blender, and if you don't care for the taste of them, just down it as one quick shot.