“Some pumpkins” or “some punkins” means something impressive or something of importance. The term became popular in 1840s in the United States.
“The people of Western Arkansas are ‘some pumpkins,’ when they get roused” was printed in the Arkansas Intelligencer (Van Buren, AR) on December 30, 1843. “Black Dog, the Osage Chief, “‘s some Punkins,’ a man of great stature” was printed in the Arkansas Intelligencer (Van Buren, AR) on May 31, 1845.
(Oxford English Dictionary)
U.S. slang. In predicative use: a person or matter of importance or consequence; an impressive thing. Esp. in some pumpkins.
1845 Spirit of Times 18 Oct. 400/2 Woulddent you like to have him to take back to Lundon; you’d jest better believe he’d be some punkins in a crowd!
a1848 G. F. A. Ruxton Life in Far West (1849) viii. 266 Afore I left the settlements I know’d a white gal, and she was some punkins.
1852 C. A. Bristed Upper Ten Thousand 216 We being punkins were of course among the invited. [Note] A slang expression of young New York for people of value and consequence.
30 December 1843, Arkansas Intelligencer (Van Buren, AR), pg. 2, col. 3:
CORRESPONDENCE. (By “S.”—ed.)
FAYETTEVILLE, Dec. 19, 1843.
The people of Western Arkansas are “some pumpkins,” when they get roused.
30 October 1844, The Constitutionalist (Vicksburg, MS), pg. 2, col. 3:
Ex-governor Tucker would say, after that essay, that Judge Taylor “Was some pumpkins in a pie!”
21 March 1845, Vicksburg (MS) Sentinel, pg. 2, col. 3:
Well, my little fellow, where were you bred?
I was never bread any where sir, I reckon I’m some punkins tho’.
31 May 1845, Arkansas Intelligencer (Van Buren, AR), pg. 2, col. 3:
Black Dog, the Osage Chief, “is some Punkins,” a man of great stature—about seven feet—powerful frame, with a voice attractive and commanding.
28 June 1845, Jeffersonian (Macon, MS), pg. 1, col. 1:
... and whereas there is a vacancy in the Governorship of the said State of Oregon; which said Simtlelon or Spifflekins can’t fill in consequence of his not being “some pumpkins” enough; ...
26 November 1849, Alexandria (VA) Gazette, pg. 4, col. 1:
Colley Cibber, the theatrical critic of the Philadelphia Pennsylvanian, gives us the history of one of those slang phrases of the day, which some how get current in society, good, bad, or indifferent, among all classes. A correspondent wanting to know the origin of “some pumpkins,” one of the latest of these vagabond expressions, and whether it is not to be found in some of the old English dramas, the Pennsylvanian critic replies, that he is not aware of the saying being incorporated in any play extant, although it can claim an existence of nearly sixty years. It originated with James Fennell the celebrated tragedian who came to this city in the year 1792. When quite a lad, Fennell in company with Dr. Mosely, and the celebrated philosopher, Mr. Walker and son, made the tour of France. Arriving at Rouen, and wishing to see all they could, thye kept peeping through the little windows. As they were passing the famous cathedral of Rouen, young Walker, peeping through his little square, exclaimed, “Look, Fennell, what immense pumpkins.” His father, who had been attentively gazing at the building, turned around, exclaiming, “God, can you be looking at pumpkins while you are passing such a cathedral as this.” Young Walker observed that he did not know what he was passing, for he could see nothing above the ground. Young Fennell could not resist the temptation of plauging Walker about the pumpkins just so, whenever they approached a stately building, or tower spire, he would invariably exclaim, “Look, Walker, there are some pumpkins!” It is almost needless to say, it became a favorite, if not a common saying, as it is to this day.
OCLC WorldCat record
Theater playbill for the Melodeon Opera Troupe in “Old Folks Concert” at the Melodeon, Washington, D.C., February 6, 1858.
Author: Henry Polkinhorn; Tom Rice; Melodeon Opera Troupe (Washington, D.C.); Melodeon (Washington, D.C.); Theater Playbills and Programs Collection (Library of Congress)
Publisher: Washington : H. Polkinhorn, Printer, 
Edition/Format: Print book : English
Melodeon, late Coombs’ Hall, Penn. av. near 10th st. M. Coombs, treasurer, J.K. Search, musical director and stage manager. Saturday evening, February 6th, 1858. 39th night of the Melodeon Opera Troupe. Burlesque on the “Old Folks Concert” to-night ... the whole to conclude with T.D. Rice’s Opera of “Negro Assurance, or, the Rival Bootblacks.”
Programme: Part First: Instrumental overture / Mestayer & Co.—
Opening Chorus: Joy, joy, Freedom to-day / Troupe—
Solo & Chorus: The grave of Uncle True / R.J. Buckley—
Comic Song: Massa is a Stingy Man / Frank Weston—
Solo & Chorus (Patriotic) The Flag of the Free / T. Stone—
Comic Song: She’s some Punkins / J.K. Search—
OCLC WorldCat record
Some pumpkins : march and two step
Author: Ed Kuhn
Publisher: Kansas City, Mo. : J.W. Jenkins’ Sons Music Co., ©1908.
Edition/Format: Musical score : No Linguistic Content
OCLC WorldCat record
Author: Liza Charlesworth; Steve Mack
Publisher: New York, NY : Scholastic,  ©2017
Series: First little comics, A.
Edition/Format: Print book : Fiction : Juvenile audience : English