Jeans: Ralph Lauren (they were a gift so I'm not sure where they are from-similar ones here at Old Navy)
The Oxford shirt is a great basic for dressing up. The Baby Gap Oxford shirt starts at 12-18 months, but you can actually find a similar one at Old Navy in white 0-3 months + or blue 6-12 months +. If you join their email list, you'll receive updates when they have sales, 30% off purchases online, etc. This shirt is something both stores typically have online so I waited until there was a sale to pick one up in blue from Baby Gap and in white from Old Navy.
Some people may not put shoes on their babies until they are walking, but I couldn't resist getting Converse for Little Man. You can also find similar ones at Old Navy.