For the main meeting, a hall with LCD projector(s) for computer connection and a PC to display the presentation files. Most people will bring talks in MS PowerPoint, Adobe PDF and/or LibreOffice Impress formats (installing LibreOffice on this machine is advised, but not essential if you give people notice). It saves time and confusion at these international meetings if the PC can be configured with English language settings (Windows menus etc.). Providing a remote control for the presentation program and a laser pointer is helpful.
Some presenters may want to use their own laptops for live demonstrations, or if they’re using a less common presentation program (e.g. Apple’s Keynote).
In a large hall speakers should use a microphone if a PA is available; a radio-microphone is preferred.
The main hall (and ideally the other meeting rooms too) should have reliable, high-bandwidth WiFi internet access since most people will bring a laptop or notebook PC and want to connect up during the meeting.
Laptop batteries don’t last more than a few hours, so there will be demand for power sockets in the hall too. If these are not available at every seat, providing extension leads spread about the room is generally a good idea and is much appreciated by attendees.
Refreshments should be available at the breaks mid-morning and mid-afternoon. If your institution can’t afford to fund these itself it is acceptable to charge attendees a fee at registration to pay for them (exhibitors funds are also helpful here). People will expect to pay for their own lunches, and also to pay to attend the conference dinner which is usually held on the evening before the last day.