Suppliers, and the contract nobody reads until later
Access times, failure terms, and who owns the risk.
Supplier arrangements determine a great deal that becomes apparent only under pressure: when they can access the site, what happens if they arrive late or not at all, who is responsible for damage, what insurance is held, and what the position is if the event is cancelled.
Cancellation terms are the ones most often skimmed and most consequential, because the circumstances in which they matter are the ones where everything else is also going wrong. Different suppliers with different terms produce a cancellation position nobody has calculated.
Access and load-in times are the ones that most often cause operational failure. Several suppliers scheduled to access the same entrance in the same hour is a routine planning error with visible consequences, and it is solved by a schedule rather than by negotiation on the day.
Insurance requirements, indemnities and liability positions differ by jurisdiction and by venue and are a matter for qualified advice rather than for a template. What is worth doing without advice is confirming that certificates are current, which is a five-minute check frequently omitted.
The other supplier detail worth confirming personally is who is actually attending. Contracts are agreed with a company and delivered by individuals, and the experienced crew who did last year's event may not be the crew allocated this time. Asking is unremarkable and occasionally changes the plan.