I was also 88 lbs at my lowest due to an eating disorder (eating 800 calories a day) and I'm 5'3" and I'm also in college. I gained weight easily eating a ton of carbs (whole wheat bread, oatmeal, apples, milk and cereal, etc.) and doing some weight lifting a few times a week. I know high carb may not be very "paleo" but you need to get to a healthy weight first. I wasn't on Paleo when I was gaining weight. But now that I've gained a reasonable amount of weight, I did switch to Paleo, still eating a lot of calories (1800-2500 a day) but now eating more fat and doing very minimal exercise. My doctor also wants me to gain more weight but I know with Paleo, my body will get to its ideal weight. I'm glad I don't look like a stick anymore.

What's wrong with eating more fat? Sure you could try gaining a load of unhealthy and utterly unnecessary weight from eating junk if that's what you need to do to stay in college, but you asked the question because you didn't want to do that.

So eat more fat with your meals, a bit more protein too if you can. Get a couple of recipes that are naturally fattier, rather than relying on trying to 'supplement' it. See how much bacon you can get in at breakfast, and if you're not exercising, do some of that to stimulate your body. You'll get hungrier, it'll get easier to eat more later in the day, and just remember to make it fat and protein to sate the hunger. Then if you still want to go faster, sure, eat more rice and potatoes.

I'm underweight, and always have been, according to the BMI - which is why I feel like the BMI is a load of bull$h*t - but that aside, when I started doing 100% paleo I accidentally lost weight, which put me in a precarious place where I could see bones I had never seen before. No matter how much I increased my intake of calorie-dense foods, nothing worked. Then several people on Paleohacks mentioned rice. It's the ONLY thing that keeps me from slipping below my usual weight. I eat rice and/or potatoes with every meal. The only thing to be cautious of is that you don't use rice/potatoes to replace vitamin-rich veggies.

I'm keenly interested in this question as someone headed into an eating disorder. Upvoted, not sure why anyone would downvote this one.

GOMAD. ton of calories, nutrient dense

Since this is sort of a medical condition, maybe you could use whey protein or raw dairy. This is a deviation from strict paleo, but it appears to work pretty well in terms of adding bodyweight. The whole purpose of milk is to get that young calf growing. If you do go the whey protein route, make sure you read the label and get the cleanest powder possible. They like putting soy and other stuff in there. The raw dairy may be even more effective in terms of gaining weight, but I seem to have a problem with casein, so I haven't tried it for any length of time.

In addition, it became very obvious to those of us who had to lose weight that liquid calories were bad for our objectives. This suggests to me that liquid calories may be very good for your objective. Lots of smoothies!