My hospital is developing/updating their response to a Mass Casualty.  We are a 250-bed community hospital with limited blood product availability,

a busy OR, ER and very busy L&D.  What are some guidelines/suggestions from other Blood Banks with similar capacity?  The project lead just wants a cooler 

of blood in the ED but I am uncomfortable with that...

Depends on the distance from transfusion service to ED/OR.  I assume you are not planning on having the cooler or refrigerator with blood in the ED on a routine basis, only when the mass casualty event occurs?  Are you the only hospital in the area, or are there other hospitals with level I or II trauma capability?  

Typically, when you have a limited blood inventory, the BB response to a mass casualty incident depends on the inventory and the incident. We have two stages here (500+ bed level 1 trauma urban hosp): an ED surge where they are expecting many patients to the ED at one time that are expected to be critically/severely injured, and the actual MCI which is when they expect more than 10 patients. The BB response to an MCI is to get 5 coolers of uncrossmatched products ready and have them available to be picked up, and basically keep that amount at the ready until we are cleared. We do 4 rbcs and 2 plasma per cooler, so this is a good amount of product. As a smaller community hospital, you may not have 20 O pos red cells to set aside like that, so you have to make up what works for you. 

Once initial coolers are ready, we start calling our local suppliers to get as much product to us as possible as soon as possible. If things go awry you'll need to be restocked sooner than later, so better get those people mobilized and couriers on their way to you! That can be difficult if the hospital is in lockdown due to the emergency, so we also work with our Security team to let those couriers in the doors. 

These are the first things I think of, hope this helps!  

We are a remote 280+ bed level 2 trauma center.  After reading about many mass casualty incidents not being able to get all the patients registered before they need transfusion, I created a process and form for taking a box of blood to ED and handing it out while recording some way to know which patient got it.  Not sure it will work.  Would depend on a supervisor or someone available to do this as everyone in the BB will be super busy already.  I had to come to the conclusion that a Las Vegas level shooting here would exceed our blood supply capacity and some patients just wouldn't be able to get transfused.  Hard reality of being rural.  For more manageable events, we would use our MTP and emergency release processes as best we could.  One challenge would be knowing where patients were being sent in our system of 3 critical access and one bigger hospital which are all 20-60 miles apart.  The big one is not in the center of the others.  We have started sending a cooler of 2 units of plasma to our "full trauma" activations (over about age 5).  If they are really bad and become MTPs, they need the plasma.  If it gets wasted it is not as dire as wasting O pos or O neg RBCs.  This requires no decisions on which Rh type to give for males and females.  We keep 2 A plasma thawed at all times for this.