The phrase "a knapsack filled with" is correct and usable in written English.
You can use it when describing the contents of a knapsack or backpack, often in a narrative or descriptive context.
Example: "She opened the knapsack filled with books, snacks, and a water bottle, ready for her day hike."
Alternatives: "a backpack loaded with" or "a bag stuffed with".
Gbessay wore a knapsack filled with case-investigation forms and kept his thumbs hooked on the chest-strap clipped across his sternum.
He recalls how a US serviceman on R&R from Vietnam delivered a knapsack filled with Thai stick to him in Hawaii and how Acapulco gold was burned yellow by the wind coming off the Pacific.
Wearing new shorts, new running shoes and a bad haircut, he said he carried no hard feelings, no chip on his shoulder, only a knapsack filled with a tent and reflective vest, nylon leggings, a sleeping bag, food, water and an A.T.M. card.
Kafka's stories would somehow lead to the spots where he had stashed a knapsack filled with sandwiches.
Ryan Fogle, a third secretary at the embassy whom the Russian government accused of being an undercover CIA agent, was reportedly intercepted by Russian federal authorities carrying a knapsack filled with disguises, money and a letter offering turncoats as much as $1 million a year for providing intelligence.
DAVID CRASS Ever since David Cross moved to Tompkins Square Park he has been walking around with tons of disgusting dogs on ropes and a big filthy knapsack filled with squatter crap and his skin is all brown and he has facial tattoos and pretends not to be a junkie that got fucked by his dad just like all the other crusties there.
Have you ever tried to find a piece of clothing in a duffel bag or knapsack filled with nothing but black items?
We went on a long walk through the jungle with the elephants and were given knapsacks filled with bananas to feed them along the way.
After that, we should concentrate on the much bigger scandal of college football that includes campus "hostesses" available for recruits, and boosters handing out knapsacks filled with cash.
People say that the advance guards of the I.M.U. are beautiful female snipers armed with the latest scopes and night-vision goggles, and that the guerrillas' knapsacks are filled with dollar bills that they distribute to the farmers who feed them.
Raoul Gonzalez opened his knapsack and pulled out a photo album filled with neatly clipped newspaper photographs and snapshots of Tito, as the fighter is called, and his father, who is his trainer.
