Never too late to start eating more, or throwing a few homemade mass shakes down each day, especially around the workout - you can get away with straight simple carbs around a workout on cycle usually.
Natty pb, honey, quick oats, protein, a fattier milk or (my preference) flavored/unflavored almond milk, bananas, berries (bananas are waaaay cheaper & the better gainer tho). Calories can be 600-1200 in one big drink with 50-60g protein no prob with all kinds of macro profiles if you pay attention to what you're using. I used to call em 'Big Boy' shakes lol. I use them on cycle if appetite isn't strong only, or I get big in the wrong way QUICK lol
If you stick with water, pb, oats, honey, bananas, & protein you can blend it in the morning & take it with you un-refrigerated anywhere, along with all kinds of nuts for more calories & fats if you want them. But drinking a couple homemade mass shakes is cheap & helps drive the total up each day. Or you can use pre-made mass powders, but usually these are expensive as heck/serving or lowwww quality nutrients - might as well blend icecream with a couple protein shakes or hit McD's each day; cheaper & waaay more enjoyable for same effect.