The adjustment problem
The usual approach is to design an activity and then offer accommodations. The trouble is that accepting one requires a person to identify themselves, in front of colleagues, as the exception — and so most people do not, and quietly have a worse time instead.
The alternative is to design so the range of participation is built in for everybody. Not 'there is a seated option for anyone who needs it', but an activity in which some roles are seated as a matter of course and nobody has to ask.
Physical access, concretely
Check the venue yourself rather than trusting a description. Step-free route from the street to the room and to the toilets, not just to the lobby. Door widths. Whether the 'accessible' entrance is round the back and requires finding someone with a key.
Inside the activity: tables at a workable height rather than standing stations, no activity that requires sustained standing, no scoring that depends on speed of movement, and seats available throughout rather than produced on request.
Avoid anything requiring a specific physical capability as the only route to participation. If an activity has one physical task, give it at least two other real roles — not spectator roles, roles that affect the outcome.
Sensory and cognitive
Loud rooms with music and several simultaneous activities exclude people with hearing difficulties and are exhausting for others. Provide a quiet room, tell people it exists at the start, and make going to it unremarkable by using it yourself.
Give instructions in writing as well as aloud, every time. This helps far more people than it appears to and costs one slide.
Avoid designs that depend on fast verbal reaction or improvisation under time pressure as the only mode of participation. Written and prepared contributions should be a first-class route, not a concession.
Publish the schedule, including what each activity will involve, before the day. For a lot of people, knowing what is coming is the difference between attending and not.
Social and cultural
Alcohol: if it is there, make the non-alcoholic option equally good and equally visible, and never build an activity around drinking. A substantial fraction of any team does not drink, for reasons that are nobody's business.
Food: collect requirements in advance and design so that every person can eat a full meal, not a token plate assembled at the end. Where food is the activity, this is not a detail — it is the activity.
Religion and holidays: seasonal events that assume one tradition exclude quietly. Neutral framing — 'end of year' rather than a specific holiday — costs nothing and is noticed by exactly the people you would want to notice.
Family and caring: events outside working hours, or requiring overnight travel, are not equally available to everyone. If you do them, make the core of the programme happen in normal hours, so that leaving at five does not mean missing the part that mattered.
Ask, but not like that
'Does anyone have any accessibility requirements?' asked to a group gets no answers. Ask individually and in advance, in writing, with examples of the kinds of things people have asked for before — that framing gives permission.
And ask what people want, not only what they need. The useful question is 'is there anything about how this is run that would make it better for you', which gets answers from people who would never describe themselves as having a requirement.