Code:
var resources[3] = { 0, 0, 0 };

#define lifetime skill1  // helper skill
#define id skill2  // type of the resource
#define amount skill3  // amount of the resource

#define wood 0
#define stone 1
#define ore 2

function resource_event()
{
  resources[my.id] += my.amount;
  my.lifetime = 0;
}

action resource_act
{
  my.emask |= (ENABLE_ENTITY | ENABLE_IMPACT);
  my.event = resource_event;

  my.lifetime = 1;
  while(my.lifetime) { wait(1); }

  wait(1);
  ent_remove(me);
}


Now you only need to set the skills of the different resource entities either in WED or through script when creating them.
You could also have one action per resource type.