I did some similar stuff for the tooth fairy thing and the present thing! So you're not alone!I forgot the tooth fairy once. It was on a Sunday night though so I said that the Tooth Fairy doesn't work Sundays. Only Monday to Friday. My daughter seemed satisfied with that answer.
As for presents, my online present order arrived a couple of weeks ago. After my kids went to bed, I unpacked the parcels and put the presents on the floor and took a picture of them. (So that I could remember what I'd bought when I went to go out shopping at the mall and avoid buying duplicates...)
The next day, my 8 year old DD went to use my iPhone. She loves the Project Life app for scrapbooking. So, she opened up the Camera Roll to add pics to her page and saw the picture of all those toys! She asked me about them and I said that they were presents for various friends/family. She seemed to believe that... Luckily, it wasn't too many gifts and not her "biggie" gifts, but I'm still sad I blew the surprise on a few of them!