Can I activate my sim before I leave thailand

[#1]

I am still in thailand and want to activate my sim before I leave is this possible 

[#2]

@bikerchic1

You can activate in advance but should avoid buying a goodybag as the month starts on date of purchase. You'll need to top up at least £10 for the activation, but for convenience you might choose to top up enough to buy your first goodybag and leave a few pounds of credit over if you need anything not covered by by goodybags.

[#3]

@bikerchic1

1) Yes as SIMs are shipped abroad they can be activated outside the UK. You can follow this https://community.giffgaff.com/t5/Getting-started/Activating-your-new-SIM/ta-p/3521635 fantastic guide on activating your new SIM. 
2) In order to complete the activation of the SIM you will be required to top up with a £10 minimum top up. 
3) Speeds should be ok however, it depends on the coverage.