Does everything you do have a negative or positive effect on your health? or are there neutral things?

Likely some neutral: This is a very interesting question. Some things we do are very positive, some slightly positive, some slightly negative ; some very negative, so within that spectrum my best guess is that some things are fairly neutral. This is complicated by the fact that what may be good for one person may be harmful for another or what may good for you one day may be harmful another day. It's a complex world!

Depends on context: Very few things have an exclusively negative or exclusively positive effect in all circumstances. For example, drinking water on a hot day is health-promoting, but too much of even that can cause death. So everything in moderation is the best approach, with the exception of certain things/behaviors which have no redeeming qualities (e.g. Tobacco use, driving without seat belt).