Calorie dense foods for hard gainers?

Hi all, I’m having a hard time eating enough through out the day, I work a job where I’m on my feet all day moving around and weight is just falling off of me. I find it hard to eat breakfast and sometimes skip lunch too, I know these meals are important but a lot of the time I simply don’t have the opportunity to eat something proper or prep something before hand. What foods or snacks would you suggest for someone in my shoes, maybe something on the go or not too heavy thanks