Magic-Users in my campaigns are able to put their sorcerous learning to work at any time by using cantrips. These aren't the cantrips detailed in any published sourcebook, and they aren't written down in the wizard's spell books either. They are extemporised instances of magic. The magic-user uses his creativity and knowledge, his years of learning, his acquired talent for manipulating the fabric of reality, and he makes magic. Very minor magic.
If using a cantrip on a creature, or something held or worn by the creature, a saving throw vs. spells is allowed the potential victim to nullify the effect. The maximum mass of an affected item is one pound. The maximum area of effect is roughly a ten foot cube (not an exact or perfect cube, of course.)
Thus, a mage makes a hand motion, utters some arcane syllables, and the log in the hearth lights. He says a few more strange words, and his breakfast dishes are clean. It's not very bright, so to look through his pantry he works his fingers and says a word, and a small bright point of light appears. It lights up an area of about 10 feet. A fly is buzzing around, distracting him, so he mutters, points a finger, and it flashes out with a pop. Bah, his little light went out when he stopped thinking about it. Through the window, he sees the bill collector. He utters an odd word, works his hands, and (with a failed save) sets a small spot on his shirt on fire.
They can't directly cause even 1 point of damage, but of course a fly or a bee doesn't have even 1 hit point. It's imagination time!