Healthy Weight Gain

Hi girls, I need your help, but i'm also painfully aware this might be unrelatable to a lot of people... so please don't eye roll when you start to read lol.

I really struggle to put on weight. I have been wanting to gain weight for a long time and people keep telling me to just add butter etc to things, but I want to gain healthy weight. 

My main struggle is that I am very rarely in one place long enough to keep fresh fruit, veg, meats etc. Has anyone any tips for girls on the go so that I can still keep up with my life, while eating good healthy foods to help me put on weight.

I have no diet restrictions (but I would like to keep my dairy intake low due to acne flare ups).

I'm 28 y/o, 5ft 1, and weigh 98-100lbs depending on the time of day. I don't have any underlying health conditions that would mean I should be struggling within weight gain, I think it is a lot to do with my lifestyle. Although I do apparently have IBS, but thankfully I haven't had a bad flare up in quite a while, (and there is no obvious reason for any flare ups that have happened).