Starting this post off by saying that I was a speed based 800 guy (I was better at the 4 than the 16 and absolutely garbage at cross), and much of my training experience and coaching advice comes from working with more speed-oriented athletes (think along the lines of 52/1:59/4:50 guys). I'm also not a fan of high mileage approaches
How you should train at this point in time (late summer?) depends on when your track season is, whether you're approaching the 8 from a more speed or more endurance side, and when you're trying to peak. Either way, most 800 runners (especially high schoolers, as that's the demographic most commonly aiming for sub 2) can benefit from cross country. The extra endurance that you'll pick up running ~50 - 55 MPW at this point in the year will separate you from the guys who sometimes fall apart the last 150m. You don't need to do a whole lot of mileage during track season (sub 2 on 30 MPW is very doable for many athletes) but building the base now is a big boon. Your biggest loss if you don't build a strong base will be in consistency: you might run 1:59 by training to run a strong 650 and then getting pulled, but you could just as easily run 2:10--if you build the base, you shouldn't ever flop that badly.
Your question, however, seems to be more geared towards the late season, when the 2:00 - 2:04 guys are trying to peak to finally dip under that magical barrier. There's a ton you can read on the training cycles you should be putting in through late summer/fall for racing in spring, but let's talk about some mid to late season workouts.
4x400@sub 60 with 5 minutes recovery is a very solid session; if you're able to get through all four repeats without extending recovery or falling off pace, you'll go sub 2 once you get in a fast race. This workout is deceptively difficult; 400s in 59 sound easy at first, but you'll start tying up by the end of #3.
I also swear by the old classic--[6 - 8]x200@28 - 30, cut across the track back to the 200 start for recovery. You should be doing this workout or workouts like it throughout the entire season just to get your body used to the pace you need to be running at. Towards the end of the season, focus on hitting all your repeats under 30 and keeping your form intact towards the end--it's easy to start to get sloppy around #6. Don't.
Finally, [2 - 3]x(2x300), first 300@goal 800 pace, second 300@400 pace, recovery 100 jog between 300s and 400 jog between sets is my personal favorite workout for gauging sub-2 fitness. This workout is really, really hard--if you're hitting the paces, the last 300s will feel pretty damn similar to the last 200 of the 8. As always, focus on keeping your form together through the end of each repeat, just as you want to be doing the final 150m of the 8. This workout is also a major confidence booster; if you have a kid who's fit enough to run sub 2 but is afraid to push with 300 to go, this workout will cure that pretty quick.
Good luck!