Fixin’ to

“Fixin’ to” (“fixing to”) is a standard feature of Southern American English and dates from at least 1843.
   
“‘Fixin’ to’ is the official verb of Texas” and “‘Fixin’ to’ is the state verb of Texas” and even “‘Fixin’ to’ is the national verb of Texas” are popular sayings.
   
   
Amazon.com
Fixin’ To Be Texan (Paperback)
by Helen Bryant  
Paperback: 256 pages
Publisher: Republic of Texas (October 25, 1998)
 
Google Books
English in the Southern United States
by Stephen J. Nagle
Cambridge University Press
2003
Pg. 106:
Grammatical features of southern speech: yall, might could, and fixin to
CYNTHIA BERNSTEIN
(...)
Yall, might could, and fixin to are what Wolfram and Fasold (174) refer to as “socially diagnostic” features, in that their use identifies social characteristics of the speaker. The terms are often avoided by well-educated Southerners conscious of speaking “standard” English in formal contexts. Otherwise, their use is spread widely among regional and social dialects within the South. They are not associated with one particular variety of Southern English, they way, for example, habitual be characterizes African-American Vernacular English (cf. Fasold 1981).
 
Wikipedia: Southern American English
Use of (a-)fixin’ to as an indicator of immediate future action.
He’s fixin’ to eat.
We’re a-fixin’ to go.   
 
Never ask a man if he is from Texas
Proper use of “fixin”

“Fixin’ to” is one of the first phrases Texas children learn. “Fixin’” is a verb like no other. For example, Terry, have you sent the omnibus proposal to the National Office yet?

Terry: No. but I’m fixin’ to.

Fixin’ to implies that Terry, while not engaged in the task at hand, is making preparations to do so. Fixin’ is an active term and is more reassuring to Bob than the phrases “I will” or “I plan to.”
 
(Oxford English Dictionary)
fix, v.
intr.  a. To intend; to arrange, get ready, make preparations, for or to do something. Also with out and up. U.S.
1716 B. CHURCH Hist. Philip’s War (1865) I. 140 He fixes for another Expedition.
1779 D. LIVERMORE in Coll. New Hampsh. Hist. Soc. (1850) VI. 335 Troops are busy in clearing and fixing for laying the foundations of the huts.
1829-1943 in WENTWORTH Amer. Dial. Dict.
1854-5 in N. E. Eliason Tarheel Talk (1956) iv. 136 Aunt Lizy is just fixing to go to church.
   
7 October 1843, Brother Jonathan, “Jonathan Slick in New York,” pg. 156:
Then there’s the great golden dishes a hangin up all round, and a drippin over with light, and chunks of gold a shinin every which way, and picters and red curtins, and red cushions on the benches, all branfired new and shinin like a gal’s face when she’s a fixin to be married.
 
January 1881, Peterson’s Magazine, pg. 57:
I felt like cryin’ all the time he was a fixin’ to go.
 
18 October 1885, Atlanta (GA) Constitution, “Betsy in Texas,” pg. 4:
When we’uns wa a fixin’ to leave New Orleans atter we had done seed all them sights that at the exposition, and found out we could git tickets to Texas so cheap, pap he was a tellin’ ol it around and struck up longer a feller name Christopher Columbus Slack, a huntin’ sombeody a gwine towards Texas, so as to send his mammy with ‘em.