Awwww mama, I feel so awful that you are going through all this. I wish I lived closer because I know our little guys would have a blast playing together! I really hope your situation improves soon, it must be awful to feel so sick all the time. I had very, very bad morning sickness with my last pregnancy but it still wasn't nearly as bad as having HG.
Some things I know Ciaran loves to do (a few have been mentioned already)
-The bath! This is his favorite and will entertain him for hours. I'm using it now when I'm too sick to function well... in fact, he spent the morning in there. I gave him a pasta strainer, some of DD's Polly Pocket dolls and a bunch of little plastic dinosaurs from the dollar store and it bought me 45 minutes of quiet. He also loves bath crayons but I have to get some more.
-A sandbox. You could do this in a big, low cardboard box in the bathtub. Add in shovels and buckets and you have a goldmine of play. Ciaran will play in our sandbox for literally hours! Sand is easily vacuumed.
-Crayola makes a bunch of different "Color Wonder" products that only color on special paper... he likes those ok and it keeps the mess down.
-Magna-Doodle... he LOVES the magna-doodle... and NO mess! :)
-Wooden puzzles with the little "handles" on each piece. My mom got some for him and he will play with those quietly on my lap for a long time.
-Books that play music, books with flaps that fold up, books with textures, etc
-Crayons and paper in his high-chair, if you have one. Ciaran is just getting to the point where he likes to use crayons and if he is at the kitchen table it is easier for everyone.
-Play-Doh if he is at the point where he won't eat it. Ciaran watches the big kids play with it so he is figuring out how to play with it without eating it...
-A kitchen drawer or low cabinet filled with misc. safe things he can have... lids, bowls, spoons, spatulas, kitchen gadgets, empty containers, soup cans, empty cracker boxes, etc
-And my FAVORITE... A BIG cardboard box!! Ciaran will play in cardboard boxes for hours!! :)
Hope this helps, mama! I wish I could do more!