Apart from the overly-creative use of abbreviations this was a very enjoyable puzzle.
Most of the definitions given are from Chambers 12th Edition. Most of the standard abbreviations used in the wordplay are shown with the unused letters in brackets e.g. CO(mpany). Definitions are underlined in the clue and only included in explanations where further information is given.
Across
1a No peg in oddly shaped hole (7)
OPENING – an anagram (oddly shaped) of NO PEG IN
5a Before being bankrupt, company had money to burn (7)
COMBUST – A slang word for being bankrupt is preceded by CO(mpany) and M(oney)
10a Anti-aircraft fire coming from RAF Lakenheath (4)
FLAK – hidden (coming from) inside RAF LAKenheath
11a Country is home to unfriendly animal (10)
CHINCHILLA – a country around (is home to) an adjective meaning unfriendly
12a Guru entertained by Goering and Hitler (6)
GANDHI – hidden (entertained by) inside GoerinG AND HItler
13a Sore knee massaged with paraffin (8)
KEROSENE – an anagram (massaged) of SORE KNEE
14a Showing ill effects of journey, black stuff used by jewellers protected from cold (3-6)
JET-LAGGED – some black stuff used to make jewellery followed by a verb meaning protected from the cold
16a Vehicle moved aimlessly (5)
MOPED – two definitions – a lightweight motorcycle and a verb meaning moved aimlessly
17a Naughty child and scout leader given temporary accommodation (5)
SCAMP – the initial letter (leader) of Scout followed by some temporary accommodation
19a With gin, coerce tipsy caretaker (9)
CONCIERGE – an anagram (tipsy) of GIN COERCE
23a Old American with a plan for shopping centre to cover rash development (8)
MARSHALL – to get the name of this American general and statesman who initiated a programme of economic aid to European countries put a shopping centre around (to cover) an anagram (development) of RASH
24a Sailor with beige checked fabric (6)
TARTAN – a charade of a sailor and a colour similar to beige
26a Individual contributing something useful to church or theatre? (5,5)
ORGAN DONOR – this individual contributes something that is useful to the operating theatre, but he could also be giving an instrument to a church, or a different kind of theatre
27a Insects in “frontless” underwear (4)
ANTS – drop the initial letter (frontless) from some underwear
28a Peacekeepers strict about Egypt ignored (7)
UNHEARD – the two-letter abbreviation for the world’s peacekeepers followed by a word meaning strict around E(gypt) – I know of no provenance for this abbreviation; the IVR code for Egypt is ET (see also my comment about 25 down)
29a Ring artist with fanciful idea (7)
CHIMERA – a ring followed by the usual abbreviation for an artist
Down
2d Use hands to examine friend’s head (7)
PALPATE – a friend followed by another word for the head
3d Man rising to receive knight with no clothes on (5)
NAKED – a man’s name reversed (rising) around (to receive) K(night)
4d Kissing cheek’s the thing to do — and good! (7)
NECKING – a charade of some cheek or xxx, the two-letter word for “the thing to do”
6d Zero marks awarded in acting awards (6)
OSCARS – O (zero) and some marks left by earlier wounds
7d Sulphur Bristol men left out for recycling (9)
BRIMSTONE – an anagram (for recycling) of BRISTO(L) MEN without the L (Left out)
8d Peace is upheld by man going to church (7)
SILENCE – IS reversed (upheld in a down clue) followed by a man’s name and the abbreviation for the Church of England
9d Now I’ll lie sick, upset with author (6,7)
WILKIE COLLINS – an anagram (upset) of NOW I’LL LIE SICK
15d Ladder under tree growing flaky deposit (9)
LIMESCALE – an old word for a ladder preceded by a type of tree
18d Embarrassment ensues when king gets stuck into strong drink after tea (7)
CHAGRIN – put the abbreviation of Rex (Latin for king) inside a colloquial word for tea and an alcoholic drink
20d Discharge of fluid from the nose is punishment for a clergyman on heroin (7)
CATARRH – a form of punishment followed by the A from the clue, the abbreviation for Right Reverend (clergyman) and H(eroin)
21d One working hard in an orchard? (7)
GRAFTER – this could be someone propagating apple trees by inserting the scions into the stocks
22d Fat queen’s food store (6)
LARDER – some fat followed by the Queens’s regnal cipher
25d Kingdom of true majesty (5)
REALM – a word meaning true followed by M(ajesty) – there are enough abbreviations that a solver needs to learn so I don’t like the use of those that only apply in a particular context, in this case Her Majesty => HM; this one is not supported by Chambers Dictionary, Chambers XWD Dictionary of Crossword Abbreviations or Bradford’s Crossword Solver’s Dictionary
Comments from solvers who are new to cryptic puzzles are more than welcome – and that doesn’t mean the usual suspects can’t add their thoughts as well!
I didn’t think twice about the “m” in REALM, but now you mention it it does seem a little naughty, especially for a Quiptic. Having said that, it was a pleasant enough solve.
Being a chess player, I keep wanting to complain about about K=Knight. Eventually I remember the honours system, a subject irrelevant to my life, which is why I find it hard to remember! I suspect some overseas solvers may feel the same.
Organ donor was a cute one!
I got off to a poor start by blithely entering PIGEON (as in “pigeonhole”) for 1ac, only to find that it didn’t fit!