Hi, thanks for playing!
"Soldier+1+ammunition" is shorthand for: "If the crew member is a soldier If the crew member makes a soldier check and they spend an ammunition, they can roll their attack at +1 (which would be +3 with their skill advantage)." If the crew member is not a soldier, or cannot/does not expend ammunition from their personal supply, then they can't use that manner to attack and must choose another (or pass).
Since it's a personal item, you can freely trade ammunition between crew members at any time, so while another character couldn't spend ammunition for the bonus, they could hand some ammunition they have to another soldier during battle.
But it occurs to me that I might need to restrict that rule a bit, since you could then just pass a totem around to fight a ghost, which wasn't the intent. Maybe during a combat, it takes that crew member's action to pass a personal item around. Anyway, notes for an update!
Glad you're enjoying the game!