In all of my years teaching, the schools never once provided an emergency kit. In a situation where I was considering a restraining order against a father, the teacher's union (not a fan!) advised me to refer to the emergency manual. I didn't have one, but the district did and had requirements for all schools to have an emergency plan. When I asked the principal about it, she said she never wanted to upset anyone, so she didn't do that, in spite of it being a district requirement.
You are a wise woman. What have you considered including in the kit you donate? Some thoughts that I have include bottled water, various snack items, wet wipes. Are there bathroom facilities in the classroom? If not, toileting could be a big issue.
Something that is becoming much more common is to be able to lock classroom doors so that intruders cannot get in. Some classrooms have window views from the hall. Being able to cover and protect those may not be easy, but could make a big difference in safety.
After a lockdown at a school is prime time to review with the administration what their safety plan is and to make suggestions to them.