When Chuck famously responds to Sarah’s admission that she “may come with some baggage” by offering to be her “very own baggage handler”(Pilot), so begins a baggage motif to figure emotional turmoil throughout the series. Most obvious, Sarah struggles with unpacking her suitcase when initially living with Chuck — signifying settling into a home — due to her itinerant childhood.
Earlier, during the arc of Sarah’s masked internal conflict between choosing Shaw or Chuck, Shaw pointedly brings a bag into Castle that Sarah left in car…and which she quickly stows out of sight while the other two look on (“Final Exam”).
Additionally, in S5 Sarah repeatedly shoulders a heavy bag she has just packed when leaving Castle while keeping her difficult secret about the baby (and then promptly dropping it with a thud upon accepting Chuck’s offer to help). Her amnesiac version similarly grabs a suit case in Castle during the finale when vengefully planning to stalk and kill Quinn alone, but after again accepting Chuck’s help, she leaves it behind without a thought.
The baggage motif expands beyond Sarah, however. In “C.A.T. Squad”, Sarah sends Chuck to the apartment to retrieve her gal pals’ luggage so that he will leave her emotional baggage re: the engagement party alone. Alas, his difficulty bringing them back to Castle implies his bungling the job.
Chuck’s own baggage during the Shaw triangle arc is implied in “Tic Tac” when he pointedly stows supplies in a pack, zips it shut, and hoists it on his back before snapping the harness shut even while Sarah urges him to never change.
Alternatively, Chuck tries to help Orion with the emotional turmoil surrounding his father’s re-entry into Ellie’s life, but when she storms out Chuck gives a bag back to his dad, who promptly gives it to Devon before dumping his concerns on his future son-in-law.