Access is any activities designed to make the convention available to persons with disabilities (PWD) who might otherwise not be able to attend or fully partake in the convention.
In the United States, most facilities are required to meet standards set by the Americans with Disabilities Act. However, high load on elevators and long distances between function rooms can be an issue for PWDs.
Larger and/or more spread-out conventions often arrange for scooter rentals, generally by advance reservation and/or by referring attendees to a rental service, to make it possible for people to get back and forth between panel items over the course of the weekend. A 2000-person convention in a compact venue might need only one or two, whereas a Worldcon typically requires dozens of scooters due to the more spread-out facilities, less-mobile demographics, and longer (and thus more exhausting) duration of the con.
Seating (especially in the elevator lines) so that people with hidden disabilities can rest, reserved seating for wheelchair users who may not be able to make it from one panel to another as quickly as other attendees, and clear paths in convention areas such as the Con Suite are all useful accommodations.
Wheelchair-accessible shuttle buses may be more expensive and less accommodating than simply paying for taxis for PWDs, if accessible taxis are available in your area, as taxis are more able to provide door-to-door service than are buses.
The most common visual accommodations are for publications. These can be provided in Braille but not all visually impaired people read Braille. Screen readers are becoming popular. Some, but not all, PDF documents can easily be read by screen readers, and there are document formats particularly designed for this as well. Having access to the program guide, souvenir book, etc., a couple of weeks ahead of time allows for reformatting the docs with a sane deadline, and for making the docs available for download ahead of time. Large print versions of documents are easy to make, and there are special fonts such as APHont designed to make large-print documents easier to read.
Web sites with accommodation for the visually handicapped and hard of hearing can be published, if thought is given to incorporating the features in the site design. There are guidelines for this published by the World Wide Web Consortium (W3C) and others.
Arisia conducts a tactile tour of its Art Show, which is very popular.
For the hard of hearing, assistive listening devices are available which transmit over FM frequencies, and some attendees have receivers for these systems. In the Boston area, NESFA has two such systems available and sometimes lends them out. Text transcription systems are also available, and Arisia sometimes provides transcription using laptops connected to a chat server.
ASL interpretation can be had in most cities. It can be expensive to provide wide interpretation for extensive programming tracks, but if you publicize to the Deaf community that you will be offering it you may see an uptick in attendance as many such communities are starved for ASL-interpreted events to attend. If contact is made early, enough interpreters can be obtained and placed were they will be best used. Arisia has in the past arranged particular program items to interpret with members of the community.
A less expensive alternative might be text transcription interpretation, where a trained typist provides a running transcript of the spoken program, much like teletext/close captioning on television. This will involve more technology support, e.g. notebook computer(s) and display screen(s), but there will probably be more trained volunteers available to do the work.