The standard is always good - flamer and ML. This gives you great versatility, able to deal with hordes fairly easily and MCs and light vehicles thanks to krak and that s8 shot. Another option is meltas - either dual melta (MG/MM) or the mg and a ml. This is for when you know you're going to be facing tons of vehicles, and not many infantry units. In general though, I would keep the meltas for those assault marines you're getting (if you take 2 BFs you can put 2 flamers in each tac. and the meltas in an assault squad, plus the DC with their own crazy shit). You could also go for dual plasma (PG + PC) for removing masses of MEQ and TEQ. This is, however, a bit more expensive, so make sure it's worth it first.
Cheers! Good luck mate
If you go down to the woods today, be wary