C8 and Q5 are both models of torches - they both take 1 x "size 18650" 3.7-4.2V LiPo Cell, although a C8 can accept an extension tube to allow it to use 2 x 18650's. You totally should check what they mean by "2 Cell" because 2 rechargeable AA's means 2.4V, 2 Alkalines = 3V both of which alternatives will power something only good enough to see where you're going pretty much right in front of you, but a C8 with 2 18650's will give you a completely clear view of anything in the centre of the beam up to at least 80m and pretty good illumination from the dimmer spill around the main beam. There's also
a cheap 2 x 18650 Zoomable Torch which will throw a focussed beam at least 120m (be warned however that the one I bought stopped working properly within 2hrs of use and now, instead of 5 modes, is stuck on full power or off - I have ordered another one though, they're that good - from this seller on ebay.com rather than ebay.co.uk you can get probably the world's best price per lumen on torches, but it takes about 2 weeks to arrive).
There are a few torches which take 3 or 4 18650's, or have a built in monster LiPo wired to several CREE XML T6 LED's in parallel, which are best categorised as pocket stars - it may just be these which the organisers are intending to forbid. Then again, a 3V limit could be interesting too - much better for keeping your night vision if you go far enough around a flank on a stealth maneuver.
Top Tip: if you mount a torch on your gun then put it on the same side of the gun as your dominant hand, so on the right if you're right handed. This is so that when people see your light and shoot at it, they will be shooting at the right hand edge of the target you present, whereas if you put it on the left of your gun, they will be shooting at your centre mass.