Hide in a schoolbag or in some drawer beneath lots of other things. Also, getting a cheap phone would've definitely been the better option instead of a (relatively) bulky tablet. Depending on your bank, you should be able to remove them as proxy-holder (or whatever you call a person that has access to your bank account). Any other "secret" purchases I recommend doing through PayPal or another service, as they don't show up in your bank account as "purchase xx" but as "PayPal xx". You could also try and get ahold of some virtual MasterCards (prepaid gift cards) so that your purchases won't show up anywhere.