It's like you just don't have money, but suddenly you realised you did put a note somewhere deep in your bag and you grab that out and just feel the mixture of being lucky and relief and pessimistic about how it could be if you hadn't put that note in. What phrase can be used to desribe this feeling?
Thank God (it wasn't any worse)!
Thank God: (spoken) be pleased or happy: Thank God no one was in the way or on the sidewalk when the bus went out of control
Thankfully (it wasn't any worse)!
thankfully: (Informal) fortunately: Thankfully she wasn't injured
Phew(, it could have been worse)!
Phew: used to express relief
Am I ever lucky!
Lucky me! (can also be meant sarcastically depending on context)
Lucky me -- and lucky you, too! (Here's the money)
All's well that ends well!
Thankfully, it looked worse than it actually is!
"Phew!" But that's not a phrase..
"Thank God!" is common.. and should pass for an acceptable applicable expression, anywhere..
"Hurrah!" or "Luckily!" are also obviously relevant.
"I knew it!" would refer back to why or what (or both) you had been been fumbling in the bag for in the first place..
Me I'd say "Yes!!!" in such a situation, on any normal earth day, at any instant of caesium decay