The W54 device:
a nuclear system which is 10.75 inches diameter (270 mm), about 15.7 inches long (400 mm), and weighs around or slightly over 50 pounds (23 kg).produced in 1961, would fit into a suitcase quite nicely. Don't tell me we haven't developed anything more compact since then.
That’s pretty small. Physical limits apply, so significantly smaller may not be possible. Minimum is about 5 pounds of material, plus a foot separating two halves, plus compressive actuators and shielding - about 50lbs in a small duffel bag.
Don’t knock it. That’s smaller & lighter than two .50 BMG guns.