A kibbutz is a collective community in Israel that was traditionally based on agriculture. For more see WIKI.
A traditional Jewish holiday dish. The recipe Pynchon describes may likely have come from Cooking Jewish by Judy Bart Kancigor (Workman Publishing, 2007):
If you attended Bar Mitzvahs in the 1950, you probably saw some permutation of this recipe on the buffet table. Tongue has fallen out of favor in the intervening decades, except on sandwiches in kosher delis, and even then it's ordered only by people old enough to remember that era. [...] Tongue has a soft, creamy texture and rich taste that is difficult to compare to anything else.
1 pickled beef tongue (about 4 pounds)
1 can (20 ounces) pineapple chunks, drained
1 cup canned pitted black cherries, drained and chopped
1/4 cup golden raisins
1 jar (10 ounces) orange marmalade
2 cups orange juice
1/2 cup (packed) light or dark brown sugar
1/4 cup distilled white vinegar
Juice of 1 lemon (about 3 tablespoons)
1/2 teaspoon dry mustard
10 gingersnaps, crushed
1/4 teaspoon kosher (coarse) salt, or to taste
Hondeling is the bargaining, or haggling, style in Israel.
blue lines on a stick
This refers to a pregnancy-test device a "stick" that a woman uses to see if she is pregnant. The device displays one blue line to indicate the test has worked. A second blue line, forming a + indicates pregnancy.  So, yup, a Pregnant Pause...
"He meets her gaze and then sits staring at her, as if she's some kind of screen..."
Crap. More Lacan references, only now Maxine's a TV with a difference: instead of tubeside, Avi is Maxiside.
A traditional Ashkenazi Jewish dish prepared from calves' feet, similar to an aspic. In Eastern Europe, Jews served p'tcha with chopped eggs on Sabbath. In the early 20th century, Jewish immigrants in the United States continued to prepare the dish, and it was often served as an appetizer at Jewish weddings. But vegan?
classical piano novelty act
a polonaise is a dance, and Chopin wrote a lot of polonaises for solo piano
"...Avi pretends to be absorbed in the television."
In In Search of Lost Time (aka Remembrance of Things Past), Marcel Proust uses madeleines to contrast involuntary memory with voluntary memory. The latter designates memories retrieved by "intelligence," that is, memories produced by putting conscious effort into remembering events, people, and places. Proust's narrator laments that such memories are inevitably partial, and do not bear the "essence" of the past. The most famous instance of involuntary memory by Proust is known as the "episode of the madeleine." Here, the Tongue triggers Ernie's involuntary memory.
Purple Drank T-shirt
Purple drank is a slang term for a recreational drug popular in the hip hop community in the southern United States, originating in Houston, Texas. Its main ingredient is prescription-strength cough syrup containing codeine and promethazine. Cough syrup is typically mixed with ingredients such as Sprite soft drink or Mountain Dew. The purplish hue of purple drank comes from dyes in the cough syrup. From WIKI.
enough dress-code violations to get thrown off the L train
The L (not "El") runs along 14th Street past the old Stuyvesant H.S. (Eric Outfield from Stuyvesant), through the East Village on its way to Brooklyn. From .
The L train goes to Williamsburg, Brooklyn, and is heavily relied on and populated by "hipsters" (meaning the 2000's version of "hipster's" as opposed to the 1950's version) who reside in Williamsburg and ride the L into the Village. So the remark refers to Windust not dressing in current hipster attire and being recognized as not belonging with hipster's on the the L train.
Just some schmatte from H&M
"Schmatte" is Yiddish for a rag. H & M Hennes & Mauritz AB (H&M) is a Swedish multinational retail-clothing company, known for its fast-fashion clothing for men, women, teenagers and children. It opened its first U.S. store in New York City, on Fifth Avenue (at 51st Street) in March 2000. As of August 2010, the company had nearly two hundred individual stores in the United States.
As Deborah Kerr, or Marni Nixon, might say, or actually sing
Marni Nixon (b. 1930) is an American soprano and playback singer for featured actresses in movie musicals. She is most famous for dubbing the singing voices of the leading actresses in films, including The King and I, West Side Story and My Fair Lady. Wiki says she earned the nickname the "Ghostess with the Mostest" because her work was often uncredited.
In 1956, she worked closely with actress Deborah Kerr to supply the star's singing voice for the film version of Rodgers & Hammerstein's The King and I, and the next year she again worked with Kerr to dub her voice in An Affair to Remember.
Again, see chapters 14 and 15, Maxine recalls going to the Paradise Garage.
9:30 Club... maybe he caught Tiny Desk Unit and Bad Brains in their local-band period... maybe the smell of the 9:30 Cologne is his last, his only link with the uncorrupted youth he was?
The 9:30 Club was a late 70's-early 80's club in Washington D.C. where as mentioned, new wave/punk bands like Tiny Desk Unit and Bad Brains once played. In a negative marketing twist, Pynchon implies here that, though seemingly unrelated, Windust's use of 9:30 Cologne and its appeal is tied with the 9:30 Club of his youth.
Maybe's ass, OK?
Another way of putting it... “Fuck all the maybe's!” In other words, all those speculations are bullshit.
Heidi, a pun on hydrophobia (= rabies).