You can easily get GF food here (e.g. Marks and Spencers) but it will come at a price.
I eat a lot of grains and pulses and was shocked to see the prices here, double (or more) than back in the UK. Nuts are also pretty pricey here. I used to buy my grains in bulk through Amazon back home, you can still do that here but postage is expensive. iHerb are good but they don't match quantity for price as US or UK Amazon do (postage notwithstanding). I brought bags of grains and nuts over as my company paid for shipping too - I also do an Amazon order for guests and have them bring stuff out.
Not sure if you eat nut butters, those are expensive here. I used to, again, buy in bulk in the UK but no way of doing that here. iHerb is cheaper than local HK stores but expensive compared to UK. Decent olive oil, balsamic etc too.
Basically anything that isn't a fruit or vegetable, bring with you. Don't bring wine, you can find stores here that sell decently priced wine and it's not as bad as you think.
Also deodorant, they don't sell my brand here in HK so you might want to check that too if you're loyal to a specific brand.
Good luck with your move!