Thinking more systematically about why the bubble tea/ injection temptation bundle worked so well:
1 . Temptation
Buying bubble tea wasn't just something I really liked -- it was something I was doing too much. I find it pretty easy to forgo most of my rewards; if I only read fiction for pleasure while at the gym, I would probably just stop reading fiction for pleasure. I think the bundling is stronger when it's not a reward you're bundling, but a real temptation, such that the "perverse" incentive of potentially reducing the enjoyable activity isn't actually perverse.
I think this can be the secret bonus power of temptation bundling! In addition to maintaining my medication schedule, I also resolved my bubble tea problem. Instead of having a big struggle every day to decide whether today it would be okay for me to have one, I just checked my calendar. Wednesday: have one, no guilty feelings! Not Wednesday: wait less than a week. Either way, I feel satisfied about sticking to a plan.
(This reinforced the medication schedule again too, since it suddenly got a lot easier to remember when Wednesday was coming up...)
2 . Timing
By the time I was outside the cafe and really hankering for bubble tea, I was already more than halfway to the clinic. Even better, the thing I most like to do with a bubble tea is go for a 10-minute walk! The specific nature of the temptation I was indulging meant that, as soon as I'd gotten my prize and now needed to go earn it, my difficult task was at its absolute easiest to accomplish.
So, even though I am extremely tempted to check Tumblr, I don't think it'll make a strong temptation bundle unless I can think of a buddy-habit that will be easy to take care of when I am sitting at my laptop feeling a little foggy-headed. Though, I bet that would be a good time to do my anti-carpal-tunnel wrist-stretching exercises...
I bet good temptation bundles could be generated from both directions: list some top temptations and figure out what beneficial actions might be able to piggyback on them; or, list some top good things you want to do, figure out what state you need to be in for that good thing to feel extra-achievable, and then see if you can tempt yourself to get into that almost-ready state.