(1) If I (had) wings, I (could) (fly) to you. ＜仮定法過去：現在の事実の反対を仮定＞
※現在の事実：I don't have wings, so I cannot fly to you.
(2) If that bag (was) (not) expensive, I (would) (buy) it. ＜仮定法過去：現在の事実の反対を仮定＞
※現在の事実：That bag is expensive, so I will not buy it.
(3) If Bob (had) (bee) careful, he (wouldn't) (have) (made) a mistake. ＜仮定法過去完了：過去の事実の反対を仮定＞
※過去の事実：Bob was not careful, so he made a mistake.

参考にしてください。