Solid toiletries are extremely useful because they are not subject to the strict liquids/gels TSA rules. You can pack as many as you want!!
My favorites are:
LUSH's Jumping Juniper SOLID Shampoo
My favorites are:
LUSH's Jumping Juniper SOLID Shampoo
LUSH's Sugar Daddy-O SOLID conditioner
Of course, there is the good old bath soap...
...and laundry bar soap...
This is a favorite: Hispano Laundy Soap
(But Castile Soap can be used for bath and laundry, if you want to pack only one bar)
Then there is the travel-sized solid deodorant...
...which I melt in the microwave and repack in a smaller container (as small as a chapstick tube)
I also like solid lotion bars, like Lush's Therapy
And for him, it's been a long education process, but he's caved in and now uses (only when traveling but I'm not complaining!) bar soap instead of bath gel,
NOTE: I have no affiliation whatsoever with the brands, products or services described in this post.