Green’s Dictionary of Slang

(US) something exceptional.

1954		J. Steinbeck Sweet Thursday (1960) 108: Did I say it was going to be a wallager? This here’s a tom-wallager! They ain’t been nothing so stupendous since the Second World War.
1956		Fort Worth Star (TX) 15 Aug. 3/1: A joyous Tom Wallager is bursting in the streets.
1960		Kingsport Times (TN) 24 Aug. 4/5: This one [i.e. a hurricane] is what John Steinbeck’s characters would call a tom wallager.