And things like coats and embroidered expensive bits of uniform - mark normally and then mark in other out of the way places too - inside a cuff, near the hem on the inside , in a sleeve or pocket. Horrible to think of but several things wander - with YR it's sometimes just because they end up getting their clothes muddled up after PE but there's always a small cohort that will swipe a nice new coat or jumper and never return it, or will cut out the name tape and sew or write their own name in. If you have names in other places too it is much easier to prove that something is yours!!!
(sorry, not a nice thought before starting)
We weren't allowed to have rucksacks in reception, just book bags, and water bottles were just shoved in and occasionally wet them all through when lids weren't done up properly. Oh and made them all out of shape too!
I also found it useful to have a lunch box that had a shoulder strap as well as a handle so that when you are collecting or dropping off you don't need to have 43 different hands for all the things your dc thrusts at you as they run out of class!
To which end, I found it useful to have one of those jute/recycleable bags that you can get from the supermarket, that was big enough to stick in the book bag, the water bottle, the snack, the sun hat, the sun lotion (for summer), the coat and jumper etc, so that I just had one bag to pick up in the morning rather than lots of bits and bobs. During term time I have a bag for each dc and their book bag and any bits that need to go into school go in it (one dc brings pe kit back each weekend now, so it gets washed and stuck straight back in his jute bag)... Makes life much easier! I also leave a couple of envelopes and a pen in there in case I need them as I've forgotten to fill in lunch money or forms or whatever, and a comb as one dc always forgets to comb their hair, so I can always make them do it on the way to school if necessary.
And if they do have a book bag, tie a bit of ribbon on the handle or put on a keyring (photo keyring of their favourite toy or themselves can be handy and unique), so it is easily identifiable amongst all of the identical bookbags.
oops going on a bit sorry, will stop now!