I would consider an inexpensive pair of canal phones to have as a backup, in addition to a higher-grade pair of canal phones or in-ear monitors (to avoid an "all your audio eggs in one basket" scenario, considering the circumstances in which you might find yourself).
Similar to the Sennheiser CX300s, but at half the cost (around $30 online), would be the Creative EP630s, a pretty good-sounding canal phone for the price. They seem durable -- no problems with mine (which I use as a backup pair) in the last year and a half (although conditions have been pretty sedate, in my case -- your circumstances will no doubt be different, what with training and deployment ... hence the suggestion for a back-up). A step-up from iBuds, plus they have the added advantages of staying put better and more comfortably in the ear than regular buds and blocking out some outside noise (not true isolators, though).
As for higher-grade in-ear earphones, I really like the excellently isolating Etymotics ER6i's, but if you're in a dusty location, the tiny filters might clog up faster. If you don't have tiny ears, consider the Future Sonics Atrio M5s (around $139.99 online, from Road Dog online via eBay ... list price $199). They're not the best-looking things out there, but they'll be in your ears, and they produce a really nice, bass-rich sound that's not bloated or overwhelmed by bass. The bass is there for when it's needed ... and highs aren't ignored, either. They provide excellent bass, and the drums, especially, come through well. They actually make my iPod Nano 2nd generation sound richer and fuller. The overall effect is very pleasing and nonfatiguing ... closer to actual headphones than most in-ears, at an excellent price considering the sound quality.
One or maybe even two five-packs of Shure black foamie ear tips should last you a year, even allowing for environment -- the (washable) foamies sound very good, are comfortable, isolate well, and last noticeabley longer than other foamies (some of which are also excellent, like Complys). Plus, the M5s come with diabolical-looking flanges that should provide sturdy backup for any foamies you use. Something to consider -- check out the long Atrio M5 thread.
The M5s would not be so great for lying on your side. The Creative canal phones, for example, would be better for that, as would the Westone UM2 (well known for its low-profile comfort and light, braided cords -- a higher-end earphone listing at $299), Ety ER6i's, and maybe some others.
There are many excellent earphones to choose from. I hope you enjoy listening to whatever you end up choosing.
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Phones (in order of purchase):
Sony MDR71, Sony MDR51, Etymotic ER6, Panasonic RP-HJ50, Shure E3C, Koss PortaPro 2, Creative EP630, Etymotic ER6i, Sennheiser PX-100, Sennheiser HD555, Future Sonics Atrio M5