It's worth at least $20. Without knowing the series (date), it's impossible to give a more specific estimate.
$50
There were no series letters on any 1929-dated US bills. A large "G" indicates that the bill was distributed through the Chicago Federal Reserve District. There's more information at the question "What is the value of a 1929 US 5 dollar Federal Reserve Note?"
$12 to $15, assuming average wear.
Without knowing details like the series (date) and condition, the best possible answer is that it's worth $20.
A date is needed. Please see the question "What is the value of a (date) US 20 dollar bill?" for more information.
In worn condition, face value only. If only slightly worn, $8 or so.
More information is needed, like series date, condition, and is it a Federal Reserve Note, Silver Certificate, Demand Note, or what?
There were no series letters on any 1929 US bills. You may be referring instead to the Federal Reserve District letter; "G" indicates your bill was distributed by the Chicago district. There's more information at the question "What is the value of a 1929 US 100 dollar Federal Reserve Note?"
As of 09/2008 auction prices are around $24.
The 1934 100-dollar bills ended with Series D. A note in good condition, with little wear can be worth about $140.
Face value only.
"A" is the highest series letter for 1928 $50 Federal Reserve Notes. "K" is most likely the Federal Reserve District letter. The series letter, if any, on US bills is next to the date. Please see the question "What is the value of a 1928 US 50 dollar Federal Reserve Note?" for more information on values.