OP - What exactly are you planning? It makes a huge difference:

1. Is this a business event where you (or your employer) are picking up the tab for rooms, food, transportation and the like? If so, are these employees, customers, and what are their expectations? E.g., does an open bar mean single malt or swill?

2, Is this personal such as a wedding?

All of this means that you have to look at who pays for what. Do you care about a room discount, if the food is included? Is there a guarantee which you must meet whether the guests show up or not?

Above all, understand that this is a business transaction. If it isn't in the contract which you will sign, it isn't part of the deal. Those sodas during a break can cost $3-7 each depending on location. Extension cords cost money. Who pays for wifi?

Everything costs and everything is a negotiation. It is a 100% guarantee that if you don't do this stuff regularly, you will miss something and it will cost more later.