In addition to cantrips, don't forget ritual spells. You can cast those all day long (not in combat though). And look for ways to make creative use of skills, both in and out of combat.
Side note: You might want to reconsider using those two spells right now. At mid- to high levels, shield is a powerhouse because it's so cheap to use; it only costs your reaction and a 1st-level slot, of which you have many. But when you only have two spell slots, you can seldom afford to burn one on a single round's worth of defense. (Though, admittedly, with 1st-level wizard hit points being what they are...)
As for magic missile, it's just laying down targeted damage. Its reliability is handy in certain cases, but if all you want to do is pop one guy in the head, you have cantrips for that.
Instead, it's best to use your spell slots on things you can only do with leveled spell slots. At very low levels, sleep is insanely good. Thunderwave offers area damage and pushback, very handy in a pinch. Out of combat, charm person is always a solid pick.