I believe many people will use the double exp weekend as an opportunity to train expensive skills as it'll cost half the gp/xp. That being said I'd invest in items related to prayer,herblore,summoning,smithing and maybe construction though there isnt much of a drive to train construction. Items like frost bones, seared ashes, unfinished potions, potion secondaries such as potato cactus and wine of zamorak, also I'd focus on the more popular potions that people will use to make overloads that's just a thought though. Mithril, adamant and rune bars. For summoning the shards won't make a change in price neither will pouches and charms are unreadable which only leaves the pouch secondaries... Talismans are a good bet mainly water talisman, secondaries for pouches that give high exp around a certain level and popular pouches maybe war tortoise shells, yak hide, raw shark and unicorn horns. Just my thoughts. Do you know the rough time the double exp weekend will arrive in?