Any good hard side case with the ability to lock it will do. It's portable so it could walk off but for keeping kids out that works.
Cleaning kits are a personal preference, I use every thing from a standard G.I issued kit to a complete kit at home. I have a G.I kit for each AR both Colts 6551 Gov A2 and 6920 that goes to the field.
The GI kit is good for basic cleaning if you should need it. The kit includes, rods, patches, CLP/Breakfree, bore & chamber brushes, tooth type brush, pipe cleaners and q-tips. I added a boresnake to one of the kits but found that I really don't use it. Really the only item I use in the field is the breakfree/CLP and most of the time it's loaned to someone else. I clean the rifle about every 1,000 rnds and haven't ever had a problem in the field. Using a good lube and lubing the right parts on an AR/M16 is crucial for reliable performance.
The GI kit cleaning rod breaks down make sure if you buy a GI kit assemble the rods and sand the seams smooth. You don't want to scratch the barrel if the rods don't align and match up.
For home I use a single piece rod that's coated, boresnake, jag and variety of cleaning / lubricating agents. I have spare bore and chamber brushes and tooth brushes in the main kit with extra patches, pipe cleaners and q-tips.
Here is a list of things to consider for your cleaning kit and is a pretty good selection for any type of firearm. This list is not all inclusive I've got more stuff but this is what I use on a somewhat regular basis.
Wipe Out
Breakfree / CLP - Must have IMO
TWB25 - Lube / Grease "currently my primary lube for all firearms a little goes a long way"
Rem Oil - great for finish but also use Breakfree / CLP
Breakfree gun scrubber - similar to brake cleaner, I don't use it very often
Bluewonder kit - I don't use it very often
Good luck in your search for a M4 type firearm. My Colts have served me very well. The mods posted a FAQ on selecting a good AR you should spend some time and go through it. Consider a Colt 6920 which is as close as you can get to the M4 w/o the select fire switch.