Is it okay to
1) Have a friend stay in a hotel room overnight when you paid for a single?
No- but you probably got overcharged to begin with.
2) Sneak food out of an all you can eat buffet?
No
3) Taking lots of ketchup packs at a fast food restaurant so you don't have to buy a bottle?
Lots? No. One or two because you had taken them but ended up not using them? Sure. My 80-something grandmother brings home creamers from McD's for her coffee at home. Hee hee - this is a woman who saves money on Social Security.
4) Take you own food into a movie theater?
Yes
5) Giving a false age for your kids to get a discount?
Guilty - DD was two months premature, so we didn't tell Disneyland she was three until her actual due date had come and gone. 
Now that she's old enough to talk and reason - and has a very well-developed sense of right and wrong - we wouldn't do that.