Also, OP, think outside of the box a little bit. Here are several items that I've had in my car that aren't suspicious that could be used as weapons:
>drum sticks
The really thick and long ones used by marching snare drum players. I'm legitimately a drummer, and I frequently carried a practice pad and pair of sticks in my car.
>empty glass Coke bottle
Not too suspicious if you generally keep a messy car. Grab it by the neck, smash it, and you've got a razor sharp weapon at your disposal.
>yard work/landscaping tools, or just tools in general
Gardening hoe, shears. Pull saw. Long reach screwdrivers. Awls. As long as you can think up a reason why you had it in your car ("I was on my way to use it for x") they shouldn't be too suspicious.
>cooking utensils
Pots, pans, knives, etc. I'm a chef, so it's pretty common for me.
With anything that's not super common for most people, try to leave the item in the packaging - that way you can say you just bought it and were too lazy to take it out of your car. This is a good excuse for why you were carrying a cast iron skillet around in your car when you were on your way to work or something.