"If 'if's and 'and's were pots and pans, there'd be no need for tinkers!" ?
Typically this would be a response to someone making excuses for themselves, as in "Sure, I was late, but IF all the traffic lights were green AND IF mom didn't call right as I was leaving AND...". Or it can be directed at dreamers, who are always wondering "what if" this and "what if" that?
A lot of people these days (myself included) hear this phrase and think, "Well, that doesn't make sense." That is, it doesn't until you learn that a "tinker" is an old-school term (14th century) for a mender of kitchen utensils, including pots and pans. :)
The original proverb goes something like this:
"If wishes were horses, beggars would ride. If turnips were swords, i'd wear one by my side. If ifs and ands were pots and pans, there'd be no need for tinkers' hands."