Adults may appreciate a cola or two. Candy should be offered sparingly, but a good gourmet chocolate bar or other elegant confection makes a tasteful addition. Unless you are certain that your gift would be well received, alcoholic beverages should not be part of the basket. A separate gift of champagne or wine may be appropriate later, but you'll want to keep the basket family-friendly. You may also consider such useful items as cutting boards or kitchen utensils.
Flowers also make an interesting offering, or small picture frames.
Toiletry items such as Kleenex or bathroom tissue may also be handy items to pack in a welcoming basket. Finally, you may want to include information about the area to new tenants. If you can obtain a city map, include it in your basket. Find valid coupons to various restaurants, or a shopper's guide to the area. Include a list of emergency numbers, including fire, police and the nearest hospital.