Here's what worked:
Latest rtl-sdr.com v.3 dongle
The workhorse during the trip, not only due to testing, but because it receives everything out of the box, without an upconverter. I'm writing a detailed post at the moment, as a teaser, let me state here and now: look no further, order one.
Cable length is my only grief, not an issue as I carried a SMArt mount as well.
USB friendly shape and longer supplied cable made life and setup so much easier; a go-to solution when I didn't want HF or felt the need to enjoy local commercial FM.
Raspberry Pi 3 with powerbank
Used for ADS-B signals by creating a local WiFi hotspot with Nooelec's 5dBi antenna, sharing information to my tablet or smartphone. Completely portable with 20,000 mAh battery bank, see a plane on the beach and have detailed information with a few taps.
Nerdism galore: you'll survive without knowing which streak in the sky does what, but every moment is transformed into a planespotting event with a mobile ADS-B station.
1. Huge telescopic: came with v.3 from rtl-sdr.com, extremely versatile.
2. Nooelec 5dBi ADS-B antenna: works extremely well as a general receiving antenna for local action, screws right onto either premium dongles. Secret favourite, looks like a WiFi antenna, can be used anywhere.
3. Medium telescopic: comes with Nooelec dongles. Used this for years, good if you don't chase faraway signals. Adjustable length is good for airband and to feel smart doing 75 divided by frequency for quarter-wave calculations.
4. Nagoya knock-off from eBay: extendable telescopic, works great, saves time rummaging around in bag for magnetic mounts for RTL-SDR dongle antennas.
Nooelec One Nine takes a few seconds to screw on, insert wire / antenna connector into terminal, done.
Space-saving, light and efficient kit
Two receivers and two magnetic mounts provide backup, antennas above cover all frequencies except weak signals on HF and the Gigahertz range.
For HF: recent v.3 in direct sampling mode, larger extendable telescopic with SMArt's magnetic mount and cable, balun One Nine via barrel adaptor.
Grab n' go: SMArt with smaller telescopic on magnetic mount, or with 5dBi. I used the 5dBi plus SMArt combo extensively, because finding a magnetic mount is just one more item on the to-do list, right after locating the aloe vera gel and putting out swimming gear to dry, whereas plugging in said combo takes 3 seconds. And looks cool.
ADS-B: Either receiver with Nooelec 5dBi antenna with RasPi 3 and power bank.
Pointless to carry
For me, or when size or weight is at a premium.
Upconverter: Heavy and cumbersome to assemble, especially when v.3 in direct sampling mode does the job on strong stations, and weak signal's incessant noise wasn't on the wish list for evening listening.
Dedicated T2FD shortwave antenna: used for testing weak signal reception, finding a syphatetic tree and erecting antenna in the dark is not an experience I'll likely repeat. Large v.3's extendable antenna on magnetic mount snaps onto balcony steel railing - done.
Additonal dongles: Had a Nano 2 Plus, Mini 2 Plus, and two generic chinese dongles along to test v.3 against competition. All performed well, and I love the Nano 2 Plus for its small size, but finding MCX to SMA pigtails or adapters was annoying after a while.
Homemade 9:1 Unun: Nooelec's One Nine is smaller, easier to connect, and nearly same performance.
Long Wire: takes up little space, but hanging it from the balcony was an extra worry. Huge telescopic on SMArt mount with v.3 in direct sampling mode was great; SDRPlay with UnUn and long wire was better, but too much hassle.
Two receivers: one rtl-sdr.com v.3 dongle and one SMArt package provides the best two receivers out there, two magnetic mounts and five antennas. Both receivers have their unique strengths and weaknesses, so I carry both. $55 seems a lot, until you're faced with the evening meal tab in a tourist restaurant.
Raspberry Pi 3: backup to main laptop, and affordable enough at $60 with accessories to leave in the car without second thoughts. ModMyPi's kit contents really work in the real world, travel adapter and 6.5 ft / 2m microUSB cable was handy.
Battery bank: $20 from eBay, soaks up sunlight to power Pi 3 above if left in back window of rental car. Rarely needed evening recharge.
Balun One Nine and connectors: maybe $15 together, makes a small difference for HF reception. Probably unwarranted, but small enough not to think whether it will fit in the bag.
Total: $150, give or take depending on where you live and supplier, which is not too bad for a computer with WiFi, two software defined radio receivers and five antennas covering DC to daylight and most man-made communication forms.