I am sorry to offend any of you that have used the "leahes", but I feel very strongly that no one should have their child tethered up like a dog. Children are people too! My husband and I took our 4 young children (four year old twins, a three year old, and a two year old) to DisneyWorld, which includes through DFW airport, to Orlando airport, and to three different Disney parks over 5 days, and back through the airports. Never once did we feel like we needed to put any of them on a leash! That was about 6 years ago. More recently, I have been the daily babysitter for a two year old and an infant, along with caring for my own two year old. Even with all three of them, we went on all kinds of outings - play area at the mall, storytimes, the park, etc. and never did I need to put them on leashes! Even at two years old, they knew that if they were to take off running from me, we would immediately leave and they would not get to play, so they usually stayed right with me. If they started to wander off, they were reminded and they would generally listen. If they didn't, we would leave. Maybe some of you can see a reason for using a leash for some rare occasion, but for the most part, I find it appalling that anyone would treat their child like a pet. Instead, try teaching them to listen, or if need be, like someone else suggested, put them in a stroller or carry the infant in a sling (a safe one!) so that your arms are free to hold your toddler's hand! For goodness sake, don't treat your child like an animal!
Now, if you would still like to listen to my advice on sippy cups, try, like a few others have suggested, a regular cup. Don't put much in them at a time so that spills aren't a big problem. If you are adamant about wanting to use sippy cups, you can try using the soft spout ones first that are more like bottle nipples. Then as he gets used to that, you can switch to the regular sippy cups. My youngest always preferred the straw cups instead of regular sippy cups, so maybe give those a try instead. They have some of those that are spill-proof as well with closing lids, that are great for long car rides or outings. Hope that helps!
-M. (mother of 5)