What are good snacks to eat in the middle of the day

So I have sensory processing disorder, which basically means some senses are super sensitive, while others are the complete opposite. This affects my eating in terms of tastes (I'm a 'picky'/sensitive eater) and also in terms of hunger. Basically I don't get hungry, and the only time I do get 'hungry' is when I feel light headed/sick, after which I go 'oops I should eat something'. Generally speaking, my eating schedule is porridge with honey and peanut butter in the morning, about 4-7 cups of tea throughout the day and then dinner at night with salad. I'm living with my parents so the meals are whatever mum cooks (usually very healthy). If I like the meal, I will eat a lot of it but otherwise I will not eat much and probably stick to salad or just skip the meal & eat Greek yoghurt.

My doctor has told me that apparently this is a really bad idea and I have to start eating more regularly but I really find it hard to remember to eat or be motivated to eat during the day if I am out (at work, uni, etc.). I'm trying to figure out some kind of snack I can take in that won't be messy and is quite small. At the moment, if i remember to pack them, I'm taking in a sesame seed bar or a plum but they are still messy and leave residue on my fingers.

What snack would be good to eat during the day that won't make a mess, is small, and will give me enough energy that I won't get lightheaded/sick?