Nico has a vet appointment tomorrow in Downtown Seattle, which is two hours away by bus (it's the closest place that will do the bloodwork he needs to stay at a birdsitter's over the winter break). The only problem is, it's been freezing out for the past couple of days (36-early 40s Fahrenheit) and I need some ideas on keeping him warm enough for the ride. His current travel cage has a couple of mesh sides and isn't super warm inside. I do have an abundance of towels i could wrap the cage in and a couple of blankets, but I'm afraid that might not keep in warm enough. I bought a few of those hand-warmers (the disposable ones that you shake) but I'm not sure they're safe. Obviously if he ingests any it would be very bad, but if I wrapped them in towels and made sure he couldn't get through to them would it be okay? I will be with him the entire trip and able to keep a close eye on him.

Carboard box (around the travelcage).

If homeless people can survive with this layer of insulation, so will your bird.
There is always the option of those single-use heatpacks of course, but you run a *huge* risk over *overheating* your bird (so do not get the handwarmer-type, use those meant for reptiles! few dollars in petshops/online).
If it is really terrible: improvise a hot (warmish) water bottle => another risk of heatstroke.

I would just go with cardboard (you can chuck it after you come back, so no "vet-bugs" will come to live in your house).
Windproof (chillfactor) and great insulation (keep birdywarmth inside)

Do not forget breathing/ ventilation holes

Bus, eh? That's a challenge...
I'd go with a bundle of blankets. Pick a spot that's warm and check the temperature with your hand now and then. I suppose that I'd have those heat-thingies handy, but you may not need them. Good for you for thinking and planning and going to all this trouble. I wish you could enlist a buddy to drive you, but hey... life happens, right? Right! You sound like a wonderfully devoted parront.
Good luck. Let us know what happens.

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yup, I would say put a cardboard box around the cage and put some towels/blankets between the cage and box. (naturally make sure there's air available) also what you can do if you don't have access to the reptile heat pads is to put some hot water in a plastic bottle and wrap it in a towel, secure it in the cage on one side so it can't move. This will allow your bird to move close to the towel if they're cold and cuddle up into it like a nest and if they get a bit too hot they can move away and cool down

Don't you guys have central heating on the bus? (We do, so it never occured to me to be a problem.)

Public transport must be a nightmare in winter.
(It always is in any other aspect of course- the waiting outside, the unreliable timetables etc.)

We do have heating on the bus, it’s just that there will probably be periods of time where we’re out in the cold (waiting for the bus, walking from the bus stop to the vet, etc) and after his chill last week I really don’t want to risk it.

Is it worth the extra expense of a taxi? Or can a friend or relative with a car give you a ride? That eliminates the "standing in the cold" concerns.

EDIT: I just realized I'm a day too late. Your appointment was today. I hope everything went smoothly and you were both comfy and warm!

Can't wait to hear that hopefully all went well..

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I would be cautious about the hot-water bottle thing--once the water cools, it could leach heat away from the bird (people have gotten hypothermia on unheated water-beds)..I would think it would stay warm over 2 hours, but not sure if your bird would move away if sleeping against the bottle. I'm kind of paranoid, so who knows!