Just keep some whey protein in shaker bottles in your car, or in your knapsack. Back when I wanted to pile on more mass, instead of eating all round the clock, I just drink whey protein during tea time instead of taking in empty calories like roti canai and teh tarik.

In addition to the usual 3 meals a day (which wasn't always regular back then, while I was a project engineer), I had one protein shake before workout, and one after workout.. one protein shake during tea time (around 3 to 4 pm, between lunch and gym time) and one more at night, around 1 hour before bedtime.

Whacking protein shakes all round the clock like that had its benefits - I found it easier to pack on mass. But it has disadvantages too - my stomach got a bit gassy at times, and my stool is always loose because of the liquid diet. I was using Myoplex, and that stuff is a little denser compared to the regular protein shakes, so it feels quite filling.