During the brightest part of the day or a steady rain, look for streams of light or water entering the attic through the roof or sheathing, which can lead to more serious damage (and critter invasions) if left unfixed. (Another sign of holes is black staining on insulation.) From inside, fill sheathing gaps with closed-cell polyurethane foam. Fix small roof leaks by caulking with tripolymer elastomeric sealant, which is compatible with asphalt shingles and resists UV rays. But don't caulk large leaks, which tend to develop around chimneys or vent stacks. For now, place a bucket underneath to catch drips and stuff an old towel in the crevices to absorb moisture. Then do a more serious repair before the first winter storm hits.