Carry small amounts of shampoo (if you'll be on the road for extended periods) in little travel bottles. Get the ones from the hotel and put your own shampoo in them. Squeeze the air out of them before you tighten the cap, and it won't ever be a problem.
Use the colgate runny toothpaste, the stuff in the clear bottles; you can get the air out of the bottle before the flight, and it won't leak, either.
Pressurized or unpressurized, I've never had a problem with any of those things leaking. Put them in a ziploc if you like, but you shouldn't have to.
For shaving cream, use gel, like Edge. You shouldn't ever have a problem there, either. I use the little mini travel ones, and always keep the cap on. For extra security, run a bit of clear tape around the joint between the cap and the can; that keeps the lid from falling off in your shaving kit and the button from being depressed.
Put something hard or firm like a soap box around your toothpaste or shampoo, so it doesn't get squeezed or crushed in luggage or under your gear, and you'll never have a problem. A little soap holder will fit both your shampoo and conditioner in one box, in separate little bottles; you can do the same thing with your toothpaste, and anything else you need to carry. Carry all the miniature items instead of full size...even with a leak, it won't go far because there isn't enough to make a mess.