I have used:
1.pb and honey on diet bread---not because it is diet, but because the smaller pieces of bread fit in a pocket easier. Usually around mile 80 or so.
2. fig newtons
3. Cliff bar cut up in pieces in my bento box for eating ease.

Last year I tried a 1/2 turkey sub I put in my special needs bag--no mayo or cheese. I knew the weather would be cooler so it worked out --no different than taking a sandwich to lunch as a kid and leaving it in my lunch box outside the classroom in Phoenix. Hubby carried 1/2 a sub in his pocket, and then had another half at the special needs. I would only recommend this if the weather is not going to be hot--else it could get stinky. PB is the safer bet.

That being said, I plan to move toward an all liquid plan just to make it easier for my next IMC

After years of stomach problems, I go easy on the gut...

Pre-race (4 hours prior): Sustained Energy
HIM: Sustained Energy on the bike, and a Hammer bar on the run
IM: SE + bar on the bike, and bar on the run

For both (and ultras) I can tolerate bananas, pretzels, animals crackers, plain potato chips, other organic bars (Lara and Luna)...and I use only water. In the end, you'll find what works for you and your stomach :)

Curious -- why do you want to go with solids?

I have done it -- PB sandwich, nutter butter cookies, gummy bears, fig newtons, energy bars, gels, etc (not all in one race). I used jersey pockets and a bento box and had plenty of room. Now I go with a liquid diet and have concentrated carbo pro.

In response to sasquatch having trouble keeping up with liquid nutrition, I found the key was having in highly concentrated and keeping nutrition separate from electrolytes and hydration. Instead of a frame of mind of having to drink enough, it is a single sip a couple times an hour.

Kylie, I'm curious about solids becuase I can't imagine 8hrs of liquid food for a HIM nevertheless 15hrs for a IM.

That makes sense. I never imagined how much better it would be for me, either. And it is something you'll want to play with in your training to nail what works for you.

For one thing to try, here is what I do:
I have 2 bottles on my frame of very concentrated carbo pro (often with a nuun tablet just for flavor). I put about 600 calories in each bottle. Then I take a single sip about every 20 minutes. I also usually have a baggie of cliff blocks or a couple gels taped to my frame just in case I want something other than liquid. Sometimes I use them, sometimes I don't.

I keep that separate from hydration and electrolytes, and I found that very important. By doing so, I can adjust my liquid (ie non-nutrition intake) based on the weather without having to change my nutrition plan. I can drink more if it's really hot, less if not so hot. And for that I use water and gatorade (or water and endurolytes if gatorade isn't tasting good to me on race day).

The nutrition part of an IM is tough, and very individual. But you can start with somethings other people have had success with, and try them and figure out what is right for you.