Most tripods have single rod cup sets available from the net,and quite cheaply too..... personally, I find it easy enough to adapt a double to a single cup rest wihout resorting to actually buying anything, a half hour in he workshop covers it.
Sand spikes, great for mobility, not really seen many anglers using them for a few years up here in Yorkshire, I use mine when beach wandering, and they are good when beach bassing, I hold the rod when fishing, and use the spike when baiting up.
Dave.