(petitioner, lawyer, determined to have unreported income from law practice; some business deductions allowed because they were substantiated, but others not allowed due to lack of substantiation; deduction for meal expense disallowed due to lack of substantiation; travel expense deduction between home office and courthouse disallowed because office in home not principal place of business under I.R.C. Sec. 280A; distant worksite exception unavailable because worksite not away from home and petitioner could not use "regular work" exception because travel not to temporary worksites; travel to and from federal courthouse substantiated and deductions allowed).