what do you take to a hotel takeover that hotels never provide

going to our first big hotel takeover in june, ireland, and im trying to overpack in the right way... ive read the venue brief and they say bring your own essentials but its vague af. so im asking the experienced lot — what have you brought that ended up being a lifesaver because the hotel didnt have it. im thinking power strip because UK hotel rooms have like two plugs, mouthwash because the tiny bottle in the bathroom is always rancid, decent hangers because theres always 4 for 2 people, but what else. also do you bring your own pillow or am i being mad...