Check you local by laws to see if you can collect it legally or ring your council.
It makes excellent liquid feed. Toms and spuds particularly like it. Seaweed feed can easily be made in an old bin, half/three quarters full of water, with a couple of pierced bags of seaweed immersed in the water and with a lid on the bin. After six weeks the liquid can be bottled up, the litre plastic milk cartons are an ideal size. Half a carton to a watering can is enough to dilute it ready for use on the garden. If it's left longer to brew than it might need watering down further.
In liquid form it can also be used as a spray to deter black/green fly. I don't think slugs and snails like it either but the jury's still out on that one. It smells very strong used in liquid form but this goes, a couple of hours after spraying.
It works well as a mulch too, put round the top of pots, it dries out very quickly, goes black, with no smell and rots down quickly.
The wet stuff from your bin can be dug into beds or mixed with compost.