Blind or low vision attendees
To welcome attendees with blind or low vision, first speak to your coaches. Someone coaching an attendee with low vision should first and foremost be flexible. An attendee with low vision may already have a screen reader set up on their machine that they are used to, so the installation party is a great opportunity for a coach to get to know this attendee's setup.
Not all attendees who have low vision are blind, so make sure that any presenters giving lightning talks are using a large font on their screen. (Remember that code in particular can be hard to read on a PowerPoint.) Ask your presenters to prepare handouts in a large font. (If your coaches are giving talks, ask them to give you a digital file in advance so you can make copies beforehand; ideally, coaches shouldn't be out money to participate in your workshop!) Ask your presenters to also remember to verbally describe any images that are in their presentations.
Make sure the web site and materials you prepare for the workshop pass the Web AIM Contrast Checker. Just feed in the hex code of the background color and the font color, and this free tool will let you know if your contrast is sufficient.
Code in particular can be hard to see for anybody. The font tends to be small and not double-spaced, so if you're doing any demonstrations on a large screen, make sure your font is very large. Finding where to enlarge the type on the command line or in a text editor can also be hard, so have your coaches walk your attendees through that. It will make it easier for them to read and debug.