What are some weekend activities that can help to slow down alzheimer's?

Brain exercises. Any activity that exercises the brain can potentially help with dementia. Word puzzles, number puzzles, reading books, even reading the newspaper can help. Once dementia has set in, it is more difficult. Engaging the person, trying to make them think can help, but once it starts even the medications available do not stop it, only slow it down, and not very well.
Physical exercise. Vigorous exercise for 30 min, 3x per wk, can slow progression of alzheimer's. Evidence for exercise benefit is better than for any other dietary or lifestyle intervention.