Let’s say you use 3 sprays per application, one to the neck and one for each wrist. That would mean 42 sprays for one application per day. At that rate, you’d use about 4ml of cologne- so you’d survive with a refillable 5ml travel container.   That’s provided you have a cologne that’s strong enough to last all day. If you use a lighter cologne, you’d probably be better off bringing a full-size bottle to make sure you always smell your best.