My son loves art supplies. Even from a young age. Play-Doh, some fun kitchen items from the dollar store to use with the playdough, a ream of paper and some crayons, paints (look online, you can find deals on tempera paints). I also love blocks for kids. There are a lot of different block sets out there. I really like unit blocks, but any kind of building toy is fine so long as your child has the ability to maniuplate it. Wait a bit on tinkertoys and lincoln logs (they have to learn pattern concepts and have fine motor skills to have success with these toys).
If you don't have a sandbox outside, that might be another great option.
Give him some seeds. Making things grow is a powerful experience for young children. Even a pot can hold some flowers like bachelors buttons or some calendula or marigolds. Easy to grow and it's fun for them to make a posy for the dinner table.
Books are our favorite gift to receive, to be truthful. I'd encourage you to find a place that has a wide selection of childrens books and take time to browse. One of my favorites for this age is "Apple Farmer Annie" by Monica Wellington. It's one kids get excited about and relate to in their way. Annie has an orchard and grows apples. Pretty simple, but great text and lively illustrations. Another great one is "The Important Book" by Margaret Wise Brown (the author of "The Runaway Bunny" and "Goodnight Moon"). The board book version of "Mike Mulligan and His Steam Shovel" (it's abridged) by Virginia Lee Burton (author of "The Little House" and "Life Story") was one of my son's regularly chosen bedtime stories at this age. The story of the anthropomorphized Mary Ann, Mike's steam shovel, and their race against time is compelling and a testament to the values of hard work and loyalty. Can you tell I like it?:)
My son is almost six and we haven't started him on a computer yet, so I really can't advise in that area. (His teacher said this wasn't necessary yet, and he's not interested. We'll have plenty of time for it later.)