Here in the UK we sterilise upto a year -
when my dd was under a year, we chose to stay in an apartment offsite so that we would have access to a microwave/kitchen and wouldbe able to sterilse them in the microwave
it is also possible to use a steam steriliser or chemical sterilisation - I don't know the brands, but in the UK you use Milton tablets which you disolve in water. They are quite portable, you just need a large tub like an ice-cream tub and the tablets - the only downside is that they have a slight smell and some babys don't like it if they aren't used to it.
Can you get a steam steriliser? That would be the easiest option - I can buy a travel sized one over here which sterilises 2 bottles at a time.
For day to day use, we would fill the sterilised bottles with cooled boiled water upto the approriate level, and then use the sachets of powder which we would add just as we mixed the bottles, so no need to worry about milk going off in the parks.
that bit was easy - but the sterilisation was a pain
Bev