This is a fun question! I used to just pack shampoo and got2b glued a few years ago. Even that wasn't the best as I used to diffuse my hair all the time but wasn't able to when we went camping.
If I'm going anywhere this summer I would pack travel sized shampoo and conditioner (I clarify once a week), and my leave-in conditioner. Those are my musts. I still have to see what works for me in the summer, but I am done buying products (for realz!), so it will have to be my HETT mousse, or any of the gels I own. Honestly, I'd probably choose Joico Joilotion (nobody has heard of this?!), it's the closest thing to FSG for me.
I'm an avid camper, so most of the time I wear a hat anyways, and my hair is chin-lengths, so I don't have much to worry about!