How about reading the local newspaper – especially the business pages – for information useful for updating existing OSM data or preparing a 'To Do' list for when the weather improves.
Examples are:- 1. New shops/businesses opening up or old ones closing down. 2. Perhaps a new building project has just got underway. 3. Who has just moved to new premises? 4. What is happening to that vacant site I noticed the other day? 5. New section of highway opened. 6. Developers advertising sections for sale on new housing subdivisions.
For building sites (tag 'landuse=construction') here are a couple of useful pages from the wiki
http://wiki.openstreetmap.org/wiki/Tag:landuse%3Dconstruction http://wiki.openstreetmap.org/wiki/Key:start_date – a future date can be entered to indicate when construction is due to finish. Might be a good idea to make a diary note around that date to check on progress so that a further update can be made.
Another 'wet day' project could be to select a local area and, if you have decent Bing imagery, add building outlines to the map. Select just a block or so and use a bit of caution combined with your local knowledge in case things have changed since the area was photographed. You are then all set to go out on a fine day and gather 'on the ground' details for all these buildings.
Finally, if you use JOSM as your editor, I highly recommend installing the 'Opening Hours' plugin. Once you have checked businesses opening hours on the web you can use this plugin to add the info to the OSM data. It makes a seemingly tedious task so simple.