The answers will be things individuals prefer to do, daily type activities, have experience doing, historic review, have in common, interactive, cognitive, lightly challenging, fun or would like to learn. Free lectures and community events. This website I just encountered might give you some ideas. http://www.caring.com/articles/activities-for-dementia-alzheimers-patients.

A search in "low cost ideas for activities with older adults" yields many ideas.

Perhaps there are community members who wish to assist and adopt a program to help out with engaging this population.

I agree with Karen's suggestion that the intervention must be tailored to the needs and desires of the individual however I wonder are you thinking of a population level intervention - i.e. whole community approach ? If so, perhaps a good place to start might be with the Lifestyle Redesign programme developed by Zemke Clarke and Jackson. While developed for middle/low income elders in the US I think the principles of the programme might well work for you  - occupation centered; tailored; focusing on participation etc. The program has a substantial body of evidence to support its impact on general health and well being. Clearly you would need to localize to your own context and this is perhaps where a community based rehabilitation framework might be useful ..again agreeing with Karen's suggestion of community collaboration; you will need to think carefully about how to ensure that the programme is relevant to the needs of the people you serve and that it will interest them. These are all general suggestions but I would be interested to hear more about the population you are targeting and then perhaps I could offer more specific ideas.