I went through several weeks in my first trimester when I barely wanted to eat. In addition to the nausea, I was also sick for 4 weeks with bad chest congestion and cough, so I had low appetite from that as well. I found that I could almost always tolerate yogurt (I personally like the fruit kind, especially peach or mango), or even better, a bowl of yogurt topped with chunks of oranges (and maybe a little wheat germ or ground almonds if I was feeling adventurous). Also plain pasta with butter, or white rice with butter, mashed potatoes with butter. There was a time there when I was going around with a box of saltine crackers and a bottle of Hansens soda with me everywhere I went, and this was all I could handle.
Often I found myself hunting around the kitchen, knowing that physically I needed to eat, but not finding anything that sounded good and so ended up eating nothing. My midwife suggested that instead of hunting around the kitchen, sit or lie down in a quiet place and close my eyes and just think about what sounds good to eat. This worked - it always made me think of something, and always meant a trip to the store (send dh if possible!).