When I broke my jaw, I got really light, because I couldn't eat anything. After the surgery, I found that on a liquid diet, I had an exceptionally difficult time taking in more than 300-500 calories a day. In 10 days after my crash before my surgery, I lost 17 pounds. So much for that cycling body.
So, I went shopping for something heavy. Fortunately, I discovered Boost and Ensure Plus. Ensure Plus is fairly balanced and packs 350 calories per bottle. If you're restricted to a liquid diet, but don't want to become malnourished, find that in your local grocery store. I drank six of those a day when I was still restricted to a liquid diet and my weight came back. Sadly, I was so happy when I could eat solid food again that I went a little bit overboard on the junk food, but that's another story.
Ensure Plus + Boost. They come in lots of flavors, don't have to be constantly refrigerated, and are available everywhere.
Good luck.