Thankfully I've never really had that problem. I'm like Nate, I can always eat.
I agree that being prepared is a big part of it. Make the time to cook your meals ahead. Also, if you're not doing so, have more shakes. It's a lot easier to get more calories in if you're not staring at a big plate of real food.
If you're a real skinny bastard, you might want to look into Cy Willson's The Skinny Bastard Diet. I've heard this one keeps you pretty hungry. But if you're not, be careful with the fat gain.