What to do with single-picture events in iPhoto?
Photos need to be part of events; deleting a photo from an event deletes the photo from your Photo Library (unlike albums where deleting the photo just removes it from the album). If I was you I'd create a 'One-Off' or 'Photos I like' event. 

You could create a big event for everything you don't want to be in its own event folder. This should let the Events feature be used for what it's designed for - organising your photos by significant dates. If Events seems like too much hassle then you can just ignore them all together, make your own albums and organise them manually. 

Personally I just use events to find photos from 'the picnic' or 'that time we went to the airport', I don't bother organising or sorting my events.