Hacking jacket, buff or fawn breeches. either shirt and tie or stock shirt and coloured stock (tied correctly not ready made - ugh!) black or brown boots. Gloves, hunting whip, garter straps and spurs.
Spurs are the correct dress - you can always wear dummy ones (ie just the bars round your ankles without the points)
Hat - depends on how often you plan to come out. The SJ style marks you out as a newbie - very welcome but not very experienced. Skull cap or beagler style - more of an old hand
garter straps fit at the top of your boots - there should be a little loop at the top of the rear seam for a thin strap to go through, buckles at the front on your knee and on traditional hunting breeches, there is a button on the breeches for the garter strap to fasten to.
most modern breeches and boots don't have any provision for garter straps because they're predominantly designed for the competition market.